Merge branch 'ld/p4-current-branch-fix'

"git p4" used "name-rev HEAD" when it wants to learn what branch is checked out; it should use "symbolic-ref HEAD". * ld/p4-current-branch-fix: git-p4: don't use name-rev to get current branch git-p4: add read_pipe_text() internal function git-p4: add failing test for name-rev rather than symbolic-ref