Fix generation of perl/perl.mak

The code generating perl/Makefile from Makefile.PL was causing trouble
because it didn't considered NO_PERL_MAKEMAKER and ran makemaker
unconditionally, rewriting perl.mak. Makemaker is FUBAR in ActiveState Perl,
and perl/Makefile has a replacement for it.

Besides, a changed Git.pm is *NOT* a reason to rebuild all the perl scripts,
so remove the dependency too.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -778,7 +778,7 @@ $(patsubst %.sh,%,$(SCRIPT_SH)) : % : %.sh
 
 $(patsubst %.perl,%,$(SCRIPT_PERL)): perl/perl.mak
 
-perl/perl.mak: GIT-CFLAGS
+perl/perl.mak: GIT-CFLAGS perl/Makefile perl/Makefile.PL
 	$(QUIET_SUBDIR0)perl $(QUIET_SUBDIR1) PERL_PATH='$(PERL_PATH_SQ)' prefix='$(prefix_SQ)' $(@F)
 
 $(patsubst %.perl,%,$(SCRIPT_PERL)): % : %.perl
@@ -907,10 +907,6 @@ $(XDIFF_LIB): $(XDIFF_OBJS)
 	$(QUIET_AR)$(RM) $@ && $(AR) rcs $@ $(XDIFF_OBJS)
 
 
-perl/Makefile: perl/Git.pm perl/Makefile.PL GIT-CFLAGS
-	(cd perl && $(PERL_PATH) Makefile.PL \
-		PREFIX='$(prefix_SQ)')
-
 doc:
 	$(MAKE) -C Documentation all