Merge branch 'sb/bisect' into pu

The internal algorithm used in "git bisect" to find the next commit
to check has been optimized greatly.

* sb/bisect: (22 commits)
  SQUASH???
  bisect: get back halfway shortcut
  bisect: compute best bisection in compute_relevant_weights()
  bisect: use a bottom-up traversal to find relevant weights
  bisect: prepare for different algorithms based on find_all
  bisect: rename count_distance() to compute_weight()
  bisect: make total number of commits global
  bisect: introduce distance_direction()
  bisect: extract get_distance() function from code duplication
  bisect: use commit instead of commit list as arguments when appropriate
  bisect: replace clear_distance() by unique markers
  bisect: use struct node_data array instead of int array
  bisect: get rid of recursion in count_distance()
  bisect: make algorithm behavior independent of DEBUG_BISECT
  bisect: make bisect compile if DEBUG_BISECT is set
  bisect: plug the biggest memory leak
  bisect: add test for the bisect algorithm
  t6030: generalize test to not rely on current implementation
  t: use test_cmp_rev() where appropriate
  t/test-lib-functions.sh: generalize test_cmp_rev
  ...

Author: gitster

Documentation/git-bisect.txt

@@ -27,6 +27,7 @@ on the subcommand:
  git bisect replay <logfile>
  git bisect log
  git bisect run <cmd>...
+ git bisect next
  git bisect help
 
 This command uses a binary search algorithm to find which commit in
@@ -66,6 +67,15 @@ checks it out, and outputs something similar to the following:
 Bisecting: 675 revisions left to test after this (roughly 10 steps)
 ------------------------------------------------
 
+Note that in cases you do not know a good commit,
+you can also start with:
+
+------------------------------------------------
+$ git bisect start
+$ git bisect bad                 # current version is bad
+$ git bisect next                # check out another commit
+------------------------------------------------
+
 You should now compile the checked-out version and test it. If that
 version works correctly, type
 
@@ -353,6 +363,20 @@ rewind the tree to the pristine state.  Finally the script should exit
 with the status of the real test to let the `git bisect run` command loop
 determine the eventual outcome of the bisect session.
 
+Bisect next
+~~~~~~~~~~~
+
+In case you have marked a commit as bad but you do not know a good
+commit, you do not have to crawl through the commit history yourself to
+find a good commit. Simply issue the command:
+
+------------
+$ git bisect next
+------------
+
+In general, the command computes the next commit for the bisection and
+checks it out.
+
 OPTIONS
 -------
 --no-checkout::