Merge branch 'ld/p4-unshelve'

"git p4 unshelve" improvements.

* ld/p4-unshelve:
git-p4: fully support unshelving changelists
git-p4: unshelve into refs/remotes/p4-unshelved, not refs/remotes/p4/unshelved
git-p4: do not fail in verbose mode for missing 'fileSize' key