t/Makefile: provide a 'valgrind' target

It is easy to forget running valgrinded tests without -v, and it is
also easy to forget to redirect the output to "tee" (lest the output
scroll out of the terminal's buffer).  Running "make valgrind" will
take care of all that.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/Makefile

@@ -38,4 +38,7 @@ full-svn-test:
 	$(MAKE) $(TSVN) GIT_SVN_NO_OPTIMIZE_COMMITS=1 LC_ALL=C
 	$(MAKE) $(TSVN) GIT_SVN_NO_OPTIMIZE_COMMITS=0 LC_ALL=en_US.UTF-8
 
-.PHONY: pre-clean $(T) aggregate-results clean
+valgrind:
+	GIT_TEST_OPTS='--valgrind -v --tee' $(MAKE) -k
+
+.PHONY: pre-clean $(T) aggregate-results clean valgrind