Correct use of perl stack macros

Further to pull #49 this is the result of an audit of the use of perl
stack macros. There were several cases where PUTBACK was being called
where the stack pointer could be out-of-date.

Also some misc. cleanup where the macros were used needlessly.

src/perl/perl-signals.c

@@ -345,7 +345,6 @@ static void perl_call_signal(PERL_SCRIPT_REC *script, SV *func,
 		}
 	}
 
-	PUTBACK;
 	FREETMPS;
 	LEAVE;
 }