Merge branch 'mm/p4-unshelve-windows-fix' into maint

The command line to invoke a "git cat-file" command from inside
"git p4" was not properly quoted to protect a caret and running a
broken command on Windows, which has been corrected.

* mm/p4-unshelve-windows-fix:
  p4 unshelve: fix "Not a valid object name HEAD0" on Windows

git-p4.py

@@ -737,7 +737,7 @@ def extractLogMessageFromGitCommit(commit):
 
     ## fixme: title is first line of commit, not 1st paragraph.
     foundTitle = False
-    for log in read_pipe_lines("git cat-file commit %s" % commit):
+    for log in read_pipe_lines(["git", "cat-file", "commit", commit]):
        if not foundTitle:
            if len(log) == 1:
                foundTitle = True