t1200: cleanup and modernize test style

t1200: cleanup and modernize test style

Many parts of the tests in t1200 are run outside the test harness,
circumventing the usefulness of -v and spewing messages to stdout when
-v isn't used. Fix these problems by modernizing the test a bit.

An extra test_done has existed since commit 6a74642 (git-commit --amend:
two fixes., 2006-04-20) leading to the last 6 tests never being run.
Remove it and teach the resolve merge test about fast-forward merges.
Also fix the last test's incorrect find command and prune before
checking for unpacked objects so we remove the unreachable conflict-marked
blob.

Finally, we remove the TODO notes, because fetch, push, and clone have
their own tests since t1200 was introduced and we're not going to add
them here 4 years later.

Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>