add a add.patch config variable

The following patches try to provide an add.patch configuration variable while keeping out of the way of other commands. To do so, an environment variable counts how often git was recursively invoked. The variable is then only considered in the first recursion.

To ensure other commands work as expected also when add.patch is set, I added a test exemplifying the case with mergetool. To confirm the same for other commands, I also reran all tests with an activated add.patch, all direct invocations of git-add in the tests augmented with --no-patch. You can reproduce this by running the following commands from the root of the git source code repository.

sed -i '/add\.patch/,/}/ {

  # pretend add.patch to always be active
  s/\(patch_interactive = \).*;/\11;/
}' builtin/add.c
find t -type f -exec sed -i ' # in all tests
  /(use\|forget\|hint/! { # exclude help texts
    # replace git add invocations, also when options are passed to git,
    # but not subcommands named add.
    s/git\( -[^ ]\+ [^ ]\+\| --[^ ]\+=[^ ]\+\)* add/& --no-patch/g
  }
  /patch mode can be activated per option/ {
    # find add.patched test now invalid and deactivate
    s/\(test_expect_\)success/\1failure/
  }
' '{}' + 

I am unsure whether I placed all the code into the correct locations, so comments are much appreciated, as well as opinions about the concept of a recursion counter in general.

Regards,
XZS.

XZS (2):
count recursion depth
add a add.patch config variable

 Documentation/config.txt               |  6 ++++++
 Documentation/git-add.txt              |  3 +++
 builtin/add.c                          |  3 +++
 cache.h                                |  1 +
 contrib/completion/git-completion.bash |  1 +
 git.c                                  | 18 ++++++++++++++++++
 t/t0001-init.sh                        |  1 +
 t/t0120-recursion-depth.sh             | 17 +++++++++++++++++
 t/t3701-add-interactive.sh             | 27 +++++++++++++++++++++++++++
 9 files changed, 77 insertions(+)
 create mode 100755 t/t0120-recursion-depth.sh

2.8.0