perl/Makefile: update NO_PERL_MAKEMAKER section

The perl modules must be copied to blib/lib so they are available for
testing.
Signed-off-by: NBrandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

perl/Makefile

@@ -22,13 +22,18 @@ clean:
 ifdef NO_PERL_MAKEMAKER
 instdir_SQ = $(subst ','\'',$(prefix)/lib)
 $(makfile): ../GIT-CFLAGS Makefile
-	echo all: > $@
-	echo '	:' >> $@
+	echo all: private-Error.pm Git.pm > $@
+	echo '	mkdir -p blib/lib' >> $@
+	echo '	$(RM) blib/lib/Git.pm; cp Git.pm blib/lib/' >> $@
+	echo '	$(RM) blib/lib/Error.pm' >> $@
+	'$(PERL_PATH_SQ)' -MError -e 'exit($$Error::VERSION < 0.15009)' || \
+	echo '	cp private-Error.pm blib/lib/Error.pm' >> $@
 	echo install: >> $@
 	echo '	mkdir -p $(instdir_SQ)' >> $@
 	echo '	$(RM) $(instdir_SQ)/Git.pm; cp Git.pm $(instdir_SQ)' >> $@
-	echo '	$(RM) $(instdir_SQ)/Error.pm; \
-	cp private-Error.pm $(instdir_SQ)/Error.pm' >> $@
+	echo '	$(RM) $(instdir_SQ)/Error.pm' >> $@
+	'$(PERL_PATH_SQ)' -MError -e 'exit($$Error::VERSION < 0.15009)' || \
+	echo '	cp private-Error.pm $(instdir_SQ)/Error.pm' >> $@
 	echo instlibdir: >> $@
 	echo '	echo $(instdir_SQ)' >> $@
 else