Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

- Move the prototype of ttymsg() into ttymsg.h. syslogd and talkd
also use this, and they shouldn't have to have their own prototypes.

- Silence warnings about constness and signedness in ttymsg(). This
includes changing the return value to a `const char *', and changing
the types of `left' and `wret' (both byte counts) to ssize_t.

Reviewed by: bde