LockCount before unlocking to prevent lock-up (indefinite wait) situation.

implementation uses CriticalSections, it would lock the input_thread by leaving
(releasing) the critical section when it didn't own it.

(needed for alarm signals in rz).

Unified the StartWithMsg# logic in the 'L' and 'F' commands and made it more
"logical".
Fixed bug when aborting the 'L' command while in const-scan or find mode;
would abort the entire read prompt.

Bugfix: binary externals (transfer protocols) now use raw terminal setup.

(in addition to the output buffer), and eats the entire packet.
outcom() now returns TXBOF if the RingBufWrite() call fails.

(*much* faster!).

Experimenting with this in sbbs to see if there are any race conditions between
threads that manipulate the I/O buffers (e.g. Ctrl-C in input_thread clears
output buffer).

- disables Ctrl-C checking in input_thread (sets rio_abortable to false)
- sends Telnet "DONT BINARY" command after executing external program
- forces text attributes back to lightgray after executing external program

pass-through bitmap.

(was preliminarily named adduser).

with intercepted stdio (fix for downloads with sz).