tests: Clarify dependencies between tests, 'aggregate-results' and 'clean'

The Makefile targets 'aggregate-results' and 'clean' pretended to be
independent.  This is not true, of course, since aggregate-results
needs the results _before_ they are removed.

Likewise, the tests should have been run already when the results are
to be aggregated.

However, as it is legitimate to run only a few tests, and then aggregate
just those results, so another target is introduced, that depends on all
tests, then aggregates the results, and only then removes the results.

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

t/Makefile

@@ -14,7 +14,8 @@ SHELL_PATH_SQ = $(subst ','\'',$(SHELL_PATH))
 T = $(wildcard t[0-9][0-9][0-9][0-9]-*.sh)
 TSVN = $(wildcard t91[0-9][0-9]-*.sh)
 
-all: pre-clean $(T) aggregate-results clean
+all: pre-clean
+	$(MAKE) aggregate-results-and-cleanup
 
 $(T):
 	@echo "*** $@ ***"; GIT_CONFIG=.git/config '$(SHELL_PATH_SQ)' $@ $(GIT_TEST_OPTS)
@@ -25,6 +26,10 @@ pre-clean:
 clean:
 	$(RM) -r 'trash directory' test-results
 
+aggregate-results-and-cleanup: $(T)
+	$(MAKE) aggregate-results
+	$(MAKE) clean
+
 aggregate-results:
 	'$(SHELL_PATH_SQ)' ./aggregate-results.sh test-results/t*-*