bisect: peel annotated tags to commits

bisect: peel annotated tags to commits

This patch fixes a bug where git-bisect doesn't handle receiving
annotated tags as "git bisect good <tag>", etc. It's a regression in
27257bc466 (bisect--helper: reimplement `bisect_state` & `bisect_head`
shell functions in C, 2020-10-15).

The original shell code called:

  sha=$(git rev-parse --verify "$rev^{commit}") ||
          die "$(eval_gettext "Bad rev input: \$rev")"

which will peel the input to a commit (or complain if that's not
possible). But the C code just calls get_oid(), which will yield the oid
of the tag.

The fix is to peel to a commit. The error message here is a little
non-idiomatic for Git (since it starts with a capital). I've mostly left
it, as it matches the other converted messages (like the "Bad rev input"
we print when get_oid() fails), though I did add an indication that it
was the peeling that was the problem. It might be worth taking a pass
through this converted code to modernize some of the error messages.

Note also that the test does a bare "grep" (not i18ngrep) on the
expected "X is the first bad commit" output message. This matches the
rest of the test script.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>