Convert more log messages to use de-duplication as solution to issue #619.

A lot more lprintf() -> errprintf() conversions will be needed to fully
realize this solution (e.g. in the mail, ftp, web, services serverss).

In printfile() and printtail() which are used by menu() and many other
functions.

These should be helpful to sysops that just want to know what file is being
displayed under what conditions (e.g. for trouble-shooting or customization
reasons).

... instead of just the file name, as was expected.

Under heavy loads, I've found periodic non-blocking lock attempts just aren't
reliable enough: in particular, on Vertrauen, the guest user account record
in the user.tab file gets read and written-to A LOT (updating stats), and
under heavy loads (especially with hundreds of web client sessions), I'd get
timeouts attempting to lock the guest record in the user.tab (after about a
minute of periodic retries) - so let's just block "forever" to get the user
record lock (or until signaled or notified of a deadlock). With this change,
I've not had any user.tab lock errors or apparent deadlocks.

Let the underlying OS/filesystem handle queuing and deadlock detection,
when supported. lock() still behaves as before: non-blocking lock attempt.

... from ERROR to WARNING, so the repeats won't be logged to error.log file
and won't (normally) be sent as notifications (e.g. emails) to the sysop. The
duplicates are identified as from the same source file and line number as the
immediately previous logged error within the last 12 hours. String comparison
doesn't really work for deduplication since if you look closely, the errors
usually are *not* exact duplicates (i.e. there's a node number or a socket
descriptor or something that uniquely identifies the user/client/session).
Repeated errors don't increment the node's error counter either.

This does not de-duplicate errors logged via other means (e.g. direct calls to
log()/lputs(),lprintf() with a severity of LOG_ERR or higher), but will
solve the majority of duplicate errors that can be logged from the terminal
server.

So this at least partially addresses issue #619.

Even though we use O_EXCL, networked file systems still sometimes allow the
secondary open() to succeed. We use record locking in xpdev's sopen()
implementation for *nix, so this lock will insure such opens (and locks) will
now fail.

This is an attempt to address occassional error on Vertrauen:
ERROR 2 (No such file or directory) renaming *.rep to *.bad

Return correct error value upon seek failure.

"performing custom action"

Normally, the sysop would set the NodeActionCustom text.dat string
to override this.

This is to be used (e.g. instead of NODE_BXFR) for sysop-custom node actions.

so that if multiple entities call these functions at the same time, they
don't retry at exactly the same times.

Add/use SOCKET_STRERROR which gets the description of the *last* socket
error.

We should start using socket_errno(true) in place of ERROR_VALUE (horribly
named macro) for comparing last socket error nubers against values/macros
from errno.h.

Eliminate get_socket_errno(), unused and redundant with socket_errno().

Addresses Clang warnings about deprecation

These functions now return a common set of non-zero error values (where
appropriate), defined in userdat.h

Don't return errno.

getnodedat() now performs a non-locked read by default.

Perform more checks of getnodedat() return value before calling putnodedat()
to avoid unintentionally zeroing out node.dab records.

Add/use unlocknodedat() method for unlocking a node.dab record without
writing.

Note: The userdat.c getnodedat() and putnodedat() still return int (i.e. 0 on
success), so that can be confusing.

It's possible now for clients to easily exceed the configured max concurrent
connections limit, even though they just get an error 429 page. Let's at least
track and log when a new highwater mark is reached.

Can't backup (make copies of) an open file.

We can't send a 4xx error (ie: client did something wrong) in
plaintext on a TLS connection.

Untested beyond a basic compile check.

Clean-up the web server config menu quite a bit by condensing options.

You can also disable filebase access by setting the vpath prefix to blank.

We have this feature for the FTP, Mail, and Terminal servers (with no default
limit) but crazy abuse of my Synchronet web servers has now made this a
necessity for Vertrauen. A limit of 2 used to be considered reasonable long
ago. Today, 10 seems fair enough. Setting to 0 will impose no max-connections
per IP address (other than the total client limit per server).

Apparently JSVAL_IS_STRING() can return true even when argv[1] is out of range
(I guess I assumed it'd alwasy be NULL or VOID/undefined) and this can lead to
crash when calling JS_ValueToString() on it.

to notify sysop (user #1) that they were paged. Previously, this was
a hard-coded string. The new string in text.dat is the same, but adds
2 BELs (CTRL-G chars) and is now customizable.

Created an sbbs_t::notify() method to make this easier to use and that
method supports @-code expansion, so this text.dat string supports @-codes
(which I used).

This addresses the feature request in issue #828 (beep the sysop in the
telegram/short message, when they're paged).

1) Initialize saverobot.name since this is checked unconditionally.
   This has a side effect of initializing everything else, but name
   is the only thing that actually matters.
2) Add a bar to the global settings menu.
   Previously, if you scrolled near the bottom and selected an option,
   after changing the option, you would jump up to the last item on
   the initial screen.
3) Fix the AreaMgr Support default value to be the current, not the
   opposite of current.
4) Use the correct variable for EchoMail Relay Filtered Messages
   setting default.

We're carefully counting the errors, but never looking at the count.

Upon any node.dab lock or read failure, this code would cause errormsg() which
would often/usually end up claling getnodedat() which would block forever trying
to acquire the ndoefile_mutex (introduced in commit b9633069, I'm not clear why).

Unlock/release the mutex *before* calling errormsg().

Don't deref that null pointer

I dislike this particular code a little less now:
- no more redundant string compares
- less deeply nested if() and for() blocks
- remove added areas from the add list, rather than zeroing out the tag
- a little more common code between areas.bbs and areas.ini handling

No functional change (I hope).