Merge branch 'al/bisect-first-parent'

Finishing touches.

* al/bisect-first-parent:
  bisect: add first-parent option to documentation

diff --combined git-bisect.sh
index c7580e51a0f9953b2a68296fedbd3cfe2f7c05e6,eefc8eec88401e12a95885c5be0b1aca3c4f329a..c28e35b0fa8039f9d9ccf0925c1e17ac79c70dbe
--- 1/git-bisect.sh
--- 2/git-bisect.sh
+++ b/git-bisect.sh
@@@ -4,7 -4,7 +4,7 @@@ USAGE='[help|start|bad|good|new|old|ter
  LONG_USAGE='git bisect help
        print this long help message.
  git bisect start [--term-{old,good}=<term> --term-{new,bad}=<term>]
-                [--no-checkout] [<bad> [<good>...]] [--] [<pathspec>...]
+                [--no-checkout] [--first-parent] [<bad> [<good>...]] [--] [<pathspec>...]
        reset bisect state and start bisection.
  git bisect (bad|new) [<rev>]
        mark <rev> a known-bad revision/
@@@ -41,7 -41,7 +41,7 @@@ TERM_GOOD=goo
  
  bisect_head()
  {
 -      if test -f "$GIT_DIR/BISECT_HEAD"
 +      if git rev-parse --verify -q BISECT_HEAD > /dev/null
        then
                echo BISECT_HEAD
        else