Document SIGLIBRT in signal(3); take a stab at the signal description as the original committer didn't provide one.
Document SIGLIBRT in signal(3); take a stab at the signal description as
the original committer didn't provide one.

MFC after:	3 days

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