Add a few more functions which are safe to call from signal handlers, and give a bit of advice.
Add a few more functions which are safe to call from signal handlers,
and give a bit of advice.

Obtained from:	OpenBSD
MFC After:	1 week

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase