I need to remove the \n at the end of usage() since puts() appends one.

hash entries will then have incorrect or invalid message numbers.

I've likely broken something though, so if you see weird behaviour with
extended ASCII, let me know please.

This is *likely* to break the Win32 build and even when the macros are
specified in xpdev, I doubt Microsoft has added support for the 'z' size
specifier used in smblib/smbadd.c we'll likely need a SIZE_T_SIZE macro
that is "z" on C99 systems and "ll" or "64" or whatever it is on Win32.

Or maybe a whole slew of complete SIZE_T macros since the 32/64 but thing
and the max file size thing may actually need the full format specification
to be in the macro... "zu" on C99 platforms and whatever magic Microsoft
needs there.

no need to do manual initialization here.

smb_faddrtoa(), smb_netaddr(), smb_subject_crc(), and smb_zonestr().

wildcards (e.g. "*.SHD").

mark found hashes and only write the not-found hashes to disk, rather than not
writing *any* hashes (when any match) because the message is a "dupe".
When update is false, the behavior is the same as before.

(using new xpdev/getfext function).
Now locks/unlocks message base for exclusive maintenance access.

Instead, the index is sorted to guarantee message numbers are indexed
sequentially. The message base may still be re-numbered using the -renumber
command-line option (not recommended).
The /m command-line option has been removed since the SMB_EMAIL status bit has
been supported for many years now.