* scmsigs.c (scm_sigaction_for_thread): Correction to signum range
        test, avoids SCM_VECTOR_REF outside bounds of signal_handlers on
        calling "(sigaction NSIG)".

This is just an off-by-one, signum==NSIG is the only bad case.  You
can provoke it under electric fence with

	(sigaction NSIG)

I see the 1.6 has no such range check at all, perhaps it'd be a good
idea.