Perl extension for consistent signal handling

 Sig::SigAction implements set_sig_handler(), which sets up a signal handler and
 (optionally) returns an object which causes the signal handler to be reset to
 the previous value, when it goes out of scope.
 .
 Also implemented is timeout_call() which takes a timeout value and a code
 reference, and executes the code reference wrapped with an alarm timeout.
 .
 Finally, two convenience routines are defined which allow one to get the
 signal name from the number -- sig_name(), and get the signal number from the
 name -- sig_number().