Bug with git merge-base and a packed ref

[Stepan Kasal <kasal@ucw.cz>]

Hello,

first, I observed a bug with git pull --rebase:
if the remote branch got rebased and the loval branch was updated,
pull tried to rebase the whole branch, not the local increment.

A reproducer would look like that

# in repo1:
git checkout tmp
cd ..
git clone repo1 repo2
cd repo1
git rebase elsewhere tmp
cd ../repo2
# edit
git commit -a -m 'Another commit'
git pull -r

The last command performs something like
   git rebase new-origin/tmp
instead of
   git rebase --onto new-origin/tmp old-origin/tmp

I'm using git version 2.10.1.windows.1


I tried to debug the issue:
I found that the bug happens only at the very first pull after clone.
I was able to reproduce it with git-pull.sh

The problem seems to be that command
  git merge-base --fork-point refs/remotes/origin/tmp refs/heads/tmp
returns nothing, because the refs are packed.

Could you please fix merge-base so that it understands packed refs?

Thanks,
  Stepan