Use template adapter to account for signal() prototype variations

[Alexandre Oliva]

On IRIX 5.2, the type of a signal handler is `void (*)(...)', so
compilation would fail.  Ok to install?

Unfortunately, there still remains a execution error on IRIX 5.2: it
appears that each division by zero triggers *two* traps, the first of
which isn't caught by the SIGFPE handler.  Within GDB, I get two
SIGFPEs, but execution of gen-num-limits results in:

Trace/BPT trap (core dumped)

when testing whether bool divide-by-zero traps.  Can anybody explain
this, and suggest how to work around it?