Merge branch 'maint-1.5.4' into maint

* maint-1.5.4: git-bisect: make "start", "good" and "skip" succeed or fail atomically git-am: cope better with an empty Subject: line Ignore leading empty lines while summarizing merges bisect: squelch "fatal: ref HEAD not a symref" misleading message builtin-apply: Show a more descriptive error on failure when opening a patch Clarify documentation of git-cvsserver, particularly in relation to git-shell