Merge branch 'master' into cc/trace

Merge branch 'master' into cc/trace

* master:
  Trace into a file or an open fd and refactor tracing code.
  Replace uses of strdup with xstrdup.
  consolidate two copies of new style object header parsing code.
  Documentation: Fix howto/revert-branch-rebase.html generation
  fmt-merge-msg: fix off-by-one bug
  git-rev-list(1): group options; reformat; document more options
  Constness tightening for move/link_temp_to_file()
  gitweb: Fix git_blame
  Include config.mak.autogen in the doc Makefile
  Use xmalloc instead of malloc
  git(7): move gitk(1) to the list of porcelain commands
  gitk: Fix some bugs in the new cherry-picking code
  gitk: Improve responsiveness while reading and layout out the graph
  gitk: Update preceding/following tag info when creating a tag
  gitk: Add a menu item for cherry-picking commits
  gitk: Fix a couple of buglets in the branch head menu items
  gitk: Add a context menu for heads
  gitk: Add a row context-menu item for creating a new branch
  gitk: Recompute ancestor/descendent heads/tags when rereading refs
  gitk: Minor cleanups