t/t3903-stash: improve testing of git-stash show
t/t3903-stash: improve testing of git-stash show

Recently, the 'stash show' functionality was broken for the case when a
stash-like argument was supplied.  Since, commit 9bf09e, 'stash show' when
supplied a stash-like argument prints nothing and still exists with a zero
status.  Unfortunately, the flaw slipped through the test suite cracks
since the output of 'stash show' was not verified to be correct.

Improve and expand on the existing tests so that this flaws is detected.

Signed-off-by: Brandon Casey <77bc9a9984e6786c5799d7a71768cf023120ef76@nrlssc.navy.mil>
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