[PATCH/RFC v3 0/4] Improving performance of git clean

I've marked this RFC since there are known problems here.

v2 of the patch can be found here: http://thread.gmane.org/gmane.comp.version-control.git/267023/focus=267023

Changes in v3:
* Created setup.c:read_gitfile_gently to use for submodule
  probing
* Cleanup of some tests by use of test_commit helper
* Added more tests of cleaning in the presence of submodules
* Reversed expectation of test for cleaning nested bare repos.
  They are now expected to be cleaned. Added one more case.
* Fixed bug where submodules could be cleaned by using new
  read_gitfile_gently for additional submodule check in
  clean.c:is_git_repository
* Attempt to change behavior of patch implementation to clean
  bare repositories (only partially successful)
* Reworded commit message of the performance fix commit

Known Problems:
* Unsure about the setup.c:read_gitfile refactor, feels a bit
  messy?
* Potentially a missing sanity check of git file size in
  setup.c:read_gitfile_gently_or_non_gently
* We still get a behavioral change for empty bare repositories
  placed in a ".git" directory. Currently we clean empty bare
  repos in a .git folder but not non-empty one. After this
  patch we won't clean either. How serious is this? Is there
  an easy fix (preferebly to clean all bare repositories)?
* Still have issues in the performance tests, see comments
  from Thomas Gummerer on v2

Thanks to Junio C Hamano and Jeff King for spotting fundamental problems in v2 and suggesting a solution.

Erik Elfström (4):
  setup: add gentle version of read_gitfile
  t7300: add tests to document behavior of clean and nested git
  p7300: add performance tests for clean
  clean: improve performance when removing lots of directories

 builtin/clean.c       |  25 ++++++++--
 cache.h               |   1 +
 setup.c               |  94 ++++++++++++++++++++++++++++---------
 t/perf/p7300-clean.sh |  37 +++++++++++++++
 t/t7300-clean.sh      | 125 ++++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 257 insertions(+), 25 deletions(-)
 create mode 100755 t/perf/p7300-clean.sh