MFC: fix situation where GDB gives incorrect backtraces when a signal      handler is in the call chain.
MFC: fix situation where GDB gives incorrect backtraces when a signal
     handler is in the call chain.

Approved by:	re(kensmith)

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