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where the stack pointer could be out-of-date.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-common.c

@@ -248,9 +248,9 @@ void irssi_callXS(void (*subaddr)(pTHX_ CV* cv), CV *cv, SV **mark)
 	dSP;
 
 	PUSHMARK(mark);
-	(*subaddr)(aTHX_ cv);
-
 	PUTBACK;
+
+	(*subaddr)(aTHX_ cv);
 }
 
 void perl_chatnet_fill_hash(HV *hv, CHATNET_REC *chatnet)