git status: not "commit --dry-run" anymore

This removes tentative "git stat" and make it take over "git status".

There are some tests that expect "git status" to exit with non-zero status
when there is something staged.  Some tests expect "git status path..." to
show the status for a partial commit.

For these, replace "git status" with "git commit --dry-run".  For the
ones that do not attempt a dry-run of a partial commit that check the
output from the command, check the output from "git status" as well, as
they should be identical.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t6040-tracking-info.sh b/t/t6040-tracking-info.sh
index 00e1de9..664b0f8 100755
--- a/t/t6040-tracking-info.sh
+++ b/t/t6040-tracking-info.sh
@@ -69,7 +69,7 @@
 		cd test &&
 		git checkout b1 >/dev/null &&
 		# reports nothing to commit
-		test_must_fail git status
+		test_must_fail git commit --dry-run
 	) >actual &&
 	grep "have 1 and 1 different" actual
 '