Merge branch 'master' into jc/cache-tree

Merge branch 'master' into jc/cache-tree

* master:
  commit-tree: allow generic object name for the tree as well.
  Makefile: remove and create xdiff library from scratch.
  t0000-basic: Add ls-tree recursive test back.
  Libified diff-index: backward compatibility fix.
  Libify diff-index.
  Libify diff-files.
  Makefile: remove and create libgit.a from scratch.
  Document the configuration file
  Document git-var -l listing also configuration variables
  rev-parse: better error message for ambiguous arguments
  make update-index --chmod work with multiple files and --stdin
  socksetup: don't return on set_reuse_addr() error
  Fix "git show --stat"
  git-update-index --unresolve
  Add git-unresolve <paths>...
  Add colordiff for git to contrib/colordiff.
  gitk: Let git-rev-list do the argument list parsing