Merge branch 'ld/p4-import-labels'

Correct "git p4 --detect-labels" so that it does not fail to create
a tag that points at a commit that is also being imported.

* ld/p4-import-labels:
  git-p4: fix P4 label import for unprocessed commits
  git-p4: do not terminate creating tag for unknown commit
  git-p4: failing test for ignoring invalid p4 labels

diff --cc git-p4.py
Simple merge