Merge branch 'jc/merge-bases-paint-fix'

"git fmt-merge-msg" (an internal helper reduce_heads() it uses) had
a severe performance regression; an empty "git pull" took forever to
finish as the result.

* jc/merge-bases-paint-fix:
  paint_down_to_common(): parse commit before relying on its timestamp

diff --cc commit.c
Simple merge