[PATCH] teaching git-add--interactive to accept a file param

Back in October a thread came up, "Proposed git mv behavioral change",
and I inadvertently suggested a new feature for git-add--interactive;
the ability to supply an optional file path parameter and jump straight
to the "patch" subcommand for that file:

<http://kerneltrap.org/mailarchive/git/2007/10/19/348229>

This small patch series implements that suggestion:

      Refactor patch_update_cmd
      Teach git-add--interactive to accept a file path to patch
      Teach builtin-add to pass a path argument to git-add--interactive
      Document optional file parameter to git-add--interactive

It applies against the current master. I've not yet submitted many
patches to Git, so please be gentle!
                        
Documentation/git-add.txt |    5 ++++-
builtin-add.c             |   16 ++++++++++------
commit.h                  |    2 +-
git-add--interactive.perl |   11 +++++++++--
4 files changed, 24 insertions(+), 10 deletions(-)