[PATCH 0/2] Support for transferring pack files in git-ssh-*

This series allows git-ssh-* to transfer objects packed into pack files in the case of updating a ref file. It is a proof-of-concept for transferring pack files in any situation where it's useful.

The general method is that the fetch() method has the option of additionally getting other objects in addition to the one specified; objects which aren't needed are specified with dont_fetch() (when it makes sense to exclude them). In this version, it only excludes an object when it is the current value of a ref file that is being updated, but further exclusions are clearly possible.

In the case of git-ssh-*, the target specifies objects to exclude, and the source responds (asynchronously) with whether or not it knows how to exclude them (i.e., whether or not it has them). If the target has gotten an object excluded, it requests a pack file instead of a single object, and the source provides all objects referenced from the given hash, excluding those specified for exclusion.

	-Daniel
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