t1010: add mktree test
t1010: add mktree test

So far mktree (which has always been a quick hack) had no test.
At least give it a bit of test coverage.

Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git