git clone (ssh://) skips detached HEAD

[Dmitry Ivankov <divanorama@gmail.com>]

For some reason git doesn't try to fetch detached HEAD object if it's
not needed by needed heads.
It could be just work on top of detached HEAD or checked out remote branch.

Steps to reproduce:
git init test && cd test
touch 1 && git add 1 && git commit -m 123
touch 2 && git add 2 && git commit -m 345
git reset --hard HEAD^
git checkout HEAD@{1}

cd ../
git clone ssh://127.0.0.1/`pwd`/test test2

remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 0 (delta 0)
Receiving objects: 100% (3/3), done.
error: Trying to write ref HEAD with nonexistant object
91dbc2403853783f637744c31036f94a66084286
fatal: Cannot update the ref 'HEAD'.

HEAD seems to be treated in a special way in various places, so
haven't found any easy patch to fix this.

And by the way, clone --no-hardlinks test test2 still goes to is_local
codepath and avoids the bug.