request-pull: warn if the remote object is not the same as the local one

request-pull: warn if the remote object is not the same as the local one

In some cases, git request-pull might be invoked with remote and
local objects that differ even though they point to the same commit.
For example, the remote object might be a lightweight tag
vs. an annotated tag on the local side; or the user might have
reworded the tag locally and forgotten to push it.

When this happens git-request-pull will not warn, because it only
checks that "git ls-remote" returns an SHA1 that matches the local
commit (known as $headrev in the script).  This patch makes
git-request-pull retrieve the tag object SHA1 while processing
the "git ls-remote" output, so that it can be matched against the
local object.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>