commit 7b254e51df2e57842487b13cf7d03b80bd737d5f
author Jonathan Nieder <jrn@google.com> Fri Oct 04 16:13:59 2013 -0700
committer Jonathan Nieder <jrn@google.com> Fri Oct 04 16:15:57 2013 -0700
tree 38b856971c4a6f7e307734d820e3dca4a905833d
parent 3488eece9f1a197aedfe41d0b3275065c4981c82

Skip non-commits when verifying access for 'add branch' operation

Some projects have refs pointing to a tree (e.g., the Linux kernel's
"refs/tags/v2.6.11"), resulting in the message

 Cannot verify permissions to commit object <commit id> in repository <repo>

as a result of exception

 IncorrectObjectTypeException: Object <tree id> is not a commit.
	at org.eclipse.jgit.revwalk.RevWalk.parseCommit(RevWalk.java:724)
	at com.google.gerrit.server.project.ProjectControl.canReadCommit(ProjectControl.java:496)
	at com.google.gerrit.server.project.RefControl.canCreate(RefControl.java:250)
	at com.google.gerrit.server.git.ReceiveCommits.parseCreate(ReceiveCommits.java:852)

when trying to create a new branch through gerrit.

Change-Id: I9be1fe5046b5db482aa8f80d02c86d3d7a973036