p4 updates.
* ld/p4-cleanup-processes:
git-p4: avoid leak of file handle when cloning
git-p4: check for access to remote host earlier
git-p4: cleanup better on error exit
git-p4: create helper function importRevisions()
git-p4: disable some pylint warnings, to get pylint output to something manageable
git-p4: add P4CommandException to report errors talking to Perforce
git-p4: make closeStreams() idempotent