Fix wrkdir heisenreference to rm in lang/perl5.

Not everyone sees this, but I regularly do, and this makes the
symptom go away...

Index: lang/perl5/Makefile
===================================================================
RCS file: /cvsroot/pkgsrc/lang/perl5/Makefile,v
retrieving revision 1.199
diff -p -u -r1.199 Makefile
--- lang/perl5/Makefile	3 Apr 2013 09:28:55 -0000	1.199
+++ lang/perl5/Makefile	23 Apr 2013 13:29:18 -0000
@@ -164,7 +164,7 @@ SUBST_MESSAGE.mirbsd-paths=	Do not use n
 # Remove a spurious workdir reference
 SUBST_CLASSES+=		rm
 SUBST_STAGE.rm=		pre-install
-SUBST_FILES.rm=		lib/Config_heavy.pl
+SUBST_FILES.rm=		config.sh
 SUBST_MESSAGE.rm=	Do not use tools version of rm.
 SUBST_SED.rm=	-e "s!^rm_try='/.*/\\.tools/bin/rm -f!rm_try='/bin/rm -f!"