This rewrite implements changes suggested on the Git developer's list [1].

The main reasons for changing the implementation include:
  - Using a combination of 'git diff --raw -z' with 'git update-index /
    checkout-index' improves support for file names with special
    characters.
  - All diff arguments are now passed on to the underlying 'git diff'.
  - File add/deletes are handled more robustly.
  - The script no longer relies on 'mktemp' or 'tar'.

Because the script still relies on 'git-mergetool--lib' to actually launch
the diff tool, a small helper shell script is needed to interface with it.

[1]: http://thread.gmane.org/gmane.comp.version-control.git/191297/focus=191343

Signed-off-by: Tim Henigan <[email protected]>

Signed-off-by: Tim Henigan <[email protected]>

If the diff includes a submodule that lives in a subdirectory of
the project, the script fails with "No such file or directory".

For example, if a submodule is located at '<repo root>/lib/sub',
the script fails when it tries to write the submodule SHA1 to
'/tmp/.../lib/sub' because the 'lib' directory does not exist.

This commit teaches diffall to create the subdirectory path in the
tmp location prior to writing the submodule file.

This closes #21 on GitHub

Signed-off-by: Tim Henigan <[email protected]>

If a submodule is dirty (i.e. has uncommitted changes) then

  'git diff' reports "<SHA1 of parent>-dirty"

while

  'git diff --raw' reports "<SHA1 of parent>"

diffall uses the '--raw' diff format, so the "dirty" flag is lost.

To make the output more closely match that of 'git diff', teach
diffall to append "-dirty" to the submodule SHA1 when needed.

This closes #22 on GitHub.

Signed-off-by: Tim Henigan <[email protected]>