_git commit object name completion

[Daniel Shahaf <d.s@xxxxxxxxxxxxxxxxxx>]

I am seeing an issues with the new __git_commit_objects completion.

In 'zsh -f':

% autoload compinit; compinit
% git reflog --all
ebca657 refs/heads/master@{0}: reset: moving to HEAD^
f82ecfc refs/heads/master@{1}: commit: m
ebca657 refs/heads/master@{2}: commit (initial): m
% git checkout f<TAB><TAB><TAB>
f82ecfc  -- [f82ecfc] m (3 minutes ago)

I expected 'f82ecfc' to be added to the command-line immediately, as
it's the only completion.  Instead, I only get the list of possible
completions and the buffer remains unmodified, no matter how many times
I press <TAB>.

Further information:

- That's in a new repository with just two commits in it: ebca657 is the root
  and f82ecfc has ebca657 as its parent, and HEAD is ebca657.

- At one point I saw _two_ suggested completions:
    f82ecfc  -- [f82ecfc] m (88 seconds ago)
    f82ecfc  -- [f82ecfc] m (89 seconds ago)

Using master, revision ff190946690b5e770721462b706029559c0f9587.

Daniel