Function handle_perror

The "what" should be fairly short, not more than about 128 characters. Because we control all the call sites to handle_perror, it is pointless to bullet-proof it for very long strings. Design note: ADR put this routine off to the side in tbb_misc.cpp instead of Task.cpp because the throw generates a pathetic lot of code, and ADR wanted this large chunk of code to be placed on a col