last-modified: verify revision argument is a commit-ish

last-modified: verify revision argument is a commit-ish

Passing a non-committish revision to git-last-modified(1) triggers the
following BUG:

    git last-modified HEAD^{tree}
    BUG: builtin/last-modified.c:456: paths remaining beyond boundary in last-modified

Fix this error by ensuring that the given revision peels to a commit.

This change also adds a test to verify git-last-modified(1) can operate
on an annotated tag. For this an annotated tag is added that points to
the second commit. But this causes ambiguous results when calling
git-name-rev(1) with `--tags`, because now two tags point to the same
commit. To remove this ambiguity, pass `--exclude=<tag>` to
git-name-rev(1) to exclude the new annotated tag.

Reported-by: Gusted <redacted>
Signed-off-by: Toon Claes <redacted>
Signed-off-by: Junio C Hamano <redacted>