Add optional parameters to the diff option "--ignore-submodules"

After thinking some time about peoples expectations and troubles with the recursive scanning of submodules, I came up with this:

What about expanding the "--ignore-submodules" option of the git diff family with three parameters:

--ignore-submodules=all : Same behavior as "--ignore-submodules",
submodules show never up as modified.

--ignore-submodules=untracked : Don't consider submodules as modified
when they only contain untracked files, but do if the commits in the superproject are different or tracked content is modified.

--ignore-submodules=dirty : Don't consider submodules as modified
when their work tree is dirty, no matter why. This is the pre 1.7.0 behavior and doesn't recurse into submodules at all.

The first patch is just a resend of a test case rename, the second contains the implementation.

To make that more useful the default could be controlled by the .git/config or .gitmodules file. So you could have two submodules:

[submodule "sub1"]
path = sub1
url = /home/me/sub1.git/
ignore = dirty
[submodule "sub2"]
path = sub2
url = /home/me/sub2.git/
ignore = untracked

Where sub1 will not be scanned for work tree modifications by "git diff" and "git status" and for sub2 any untracked files inside the submodule will be ignored. And then "git status" should learn the "--ignore-submodule" option too. With a fourth parameter "none" it would be possible to override the defaults from the configuration anyway you want.

Opinions?

Jens Lehmann (2):
git diff: rename test that had a conflicting name
Add optional parameters to the diff option "--ignore-submodules"

 Documentation/diff-options.txt                     |   10 ++-
 diff-lib.c                                         |    1 +
 diff.c                                             |   11 +++-
 diff.h                                             |    1 +
 t/t4027-diff-submodule.sh                          |   20 ++++-
 ...submodule.sh => t4041-diff-submodule-option.sh} |   81 ++++++++++++++++++++
 6 files changed, 118 insertions(+), 6 deletions(-)
 rename t/{t4041-diff-submodule.sh => t4041-diff-submodule-option.sh} (74%)