[PATCH 0/5] Better error messages for checkout and merge.

This is a resurection of an old patch serie by Diane Gasselin:

http://thread.gmane.org/gmane.comp.version-control.git/149173/focus=149186

In short, when you have several untracked files that conflict with a merge or checkout, Git currently reports just the first. After this patch serie, it reports things like:

error: Your local changes to the following files would be overwritten by checkout:
	rep/two
	rep/one
Please, commit your changes or stash them before you can switch branches.

most of the job is done by "unpack_trees: group error messages by type", but this needed a bit of preparation to be implementable cleanly.

Compared to previous version, there are many small cleanups, and:

* unpack_trees_options was a struct, it's now an array. This makes the
  code much cleaner whenever one tries to do clever things with it.
  That's patch "Turn unpack_trees_options.msgs into an array + enum".

* A message was previously a type + an action ("removed" or
  "overwritten"). The type now encompasses the action. This duplicates
  a few lines in the declaration of the error messages, but again
  makes the rest of the code much simpler. That's patch
  "merge-recursive: distinguish "removed" and "overwritten" messages"

* The info on whether traverse_trees should stop at the first error
  was stored in info->data, with a very fragile cast to
  (unpack_trees_options *). I added one more field in the info
  structure to get rid of this cast.

Diane Gasselin (2):
  merge-recursive: porcelain messages for checkout
  t7609: test merge and checkout error messages

Matthieu Moy (3):
  Turn unpack_trees_options.msgs into an array + enum
  merge-recursive: distinguish "removed" and "overwritten" messages
  unpack_trees: group error messages by type

 Documentation/technical/api-tree-walking.txt |    2 +
 builtin/checkout.c                           |    3 +-
 builtin/merge.c                              |    3 +-
 merge-recursive.c                            |   62 +++++++----
 merge-recursive.h                            |    7 +-
 t/t3030-merge-recursive.sh                   |    2 +-
 t/t3400-rebase.sh                            |    3 +-
 t/t3404-rebase-interactive.sh                |    3 +-
 t/t7609-merge-co-error-msgs.sh               |  125 ++++++++++++++++++++++
 tree-walk.c                                  |   11 ++-
 tree-walk.h                                  |    1 +
 unpack-trees.c                               |  148 ++++++++++++++++++++------
 unpack-trees.h                               |   34 ++++--
 13 files changed, 332 insertions(+), 72 deletions(-)
 create mode 100755 t/t7609-merge-co-error-msgs.sh