Fix incorrect Coverity issue that speculates this may return fval.

This was the behavior for all string input in SBBS until recently
(Commit 55ccda62), with this change, an exception is being
made for message subjects, but the vast majority of other string
input is still limited to single-byte (i.e. US-ASCII or CP437)
characters.

This should fix issue #720

The first fix was to copy the right value, the second fix was to
ensure zero-length strings are terminated.

Also, fix macro name collision with GetDiskFreeSpaceEx

There's still outstanding issues in Coverity around sftp_state and
sftp_channel that need some deep thought, but this one is trivial.

Prevents buffer overlow with manually edited or corrupted files.

This way, WMs that enforce aspect ratio etc, won't get potentially
block the update.

A hex nybble is not 8 bits, and C strings need to be termianted.

This is a very crazy lock/unlock pattern... an extra assignment
makes it easier to follow the logic.

This should also resolve a conspiracy Coverity has about two input
threads running at the same time.

This is likely what make the old broken values appear to work.

does when compiled with mingw32.

Use "anything else" to convert hex to char.

Fixes crash when built without X11 or SDL, but with GDI (not default)

Changing a command shell or an external editor's internal code will revert
the preference of any user's that have selected that shell or editor as their
default/preference. A sysop may not realize this, so warn them with lots of
detail in the help text if they need it. See issue #721 for details.

Also updated the help text for command shell internal codes since it still
only mentioned Baja/.bin modules.

CSI=255h was not entering doorway mode anymore.

Basically everywhere was off by one.

Also, fix the get dpi size thingie to correct for window decorations.
We never actually use the result of this, but Windows might for
outline dragging or something... you can never know.

The extraction destination directory must be specified with the 'w=' option.

As Fernando Toledo (@Ragnarok) pointed out:
#524 (comment 4867)

So do more terrible hackery.