UploadPack: Verify clients send only commits for shallow lines
If a client mistakenly tries to send a tag object as a shallow line
JGit blindly assumes this is a commit and tries to parse the tag
buffer using the commit parser. This can cause an obtuse error like:
InvalidObjectIdException: Invalid id: t
c0ff331234...
The "t" comes from the "object
c0ff331234..." line of the tag tring
to be parsed as though it where the "tree" line of a commit.
Run any client supplied shallow lines through the RevWalk to lookup
the object types. Fail fast with a protocol exception if any of them
are non-commit.
Skip objects not known to this repository. This matches behavior
with git-core's upload-pack, which sliently skips over any shallow
line object named by the client but not known by the server.
Change-Id: Ic6c57a90a42813164ce65c2244705fc42e84d700