Include signal.h where reasonable and make signal handlers match

Include signal.h where reasonable and make signal handlers match
what signal(3)'s prototype says (and cast when not).
Also change MAXFOO+1 -> MAXFOO since MAXFOO includes the NULL.
Support $TMPDIR and use utime(3) not utimes(2) for portability's sake.
Don't spew "Passive mode enabled/disabled" unless verbose (this means
togglevar() needs to watch for a NULL 'message').