Merge branch 'maint'

* maint:
  commit: discard index after setting up partial commit
  filter-branch: handle filenames that need quoting
  diff: Fix miscounting of --check output
  hg-to-git: fix parent analysis
  mailinfo: feed only one line to handle_filter() for QP input
  diff.c: add "const" qualifier to "char *cmd" member of "struct ll_diff_driver"
  Add "const" qualifier to "char *excludes_file".
  Add "const" qualifier to "char *editor_program".
  Add "const" qualifier to "char *pager_program".
  config: add 'git_config_string' to refactor string config variables.
  diff.c: remove useless check for value != NULL
  fast-import: check return value from unpack_entry()
  Validate nicknames of remote branches to prohibit confusing ones
  diff.c: replace a 'strdup' with 'xstrdup'.
  diff.c: fixup garding of config parser from value=NULL

diff --cc builtin-commit.c
Simple merge

diff --cc cache.h
Simple merge

diff --cc config.c
Simple merge

diff --cc diff.c
Simple merge