[PATCH 0/3] fix unparsed object access in upload-pack

This series fixes the issue I mentioned recently with upload-pack, where we might feed unparsed objects to the revision parser. The bug is in 435c833 (the tip of the jk/peel-ref topic), which is in v1.8.1 and up.

The fix should go to maint. The bug breaks shallow clones from repositories with packed refs, though the effects range from working OK to sending too many objects to calling die() in the revision traversal machinery. Given the size of the breakage (I had several bug reports within a few hours of deploying v1.8.1.5 on github.com), and the fact that the bug was introduced only in v1.8.1, it may make sense to roll a v1.8.1.6 in addition to putting it on the 1.8.2 maint track.

  [1/3]: upload-pack: drop lookup-before-parse optimization

    This is just a cleanup, and is not necessary for the fix.

  [2/3]: upload-pack: make sure "want" objects are parsed

    This is the fix itself, which can stand alone from the other two
    patches, both semantically and textually.

  [3/3]: upload-pack: load non-tip "want" objects from disk

    While investigating the bug, I found some weirdness around the
    stateless-rpc check_non_tip code. As far as I can tell, that code
    never actually gets triggered. It's not too surprising that we
    wouldn't have noticed, because it is about falling back due to a
    race condition. But please sanity check my explanation and patch.

-Peff