Merge branch 'maint'

* maint:
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

diff --cc builtin-apply.c
Simple merge

diff --cc git-bisect.sh
Simple merge