BUG: Use GNU Short Option Style "clumping" rules not obeyed for `git stash`

``` % git stash -ku error: unknown option for 'stash save': -ku (...) % git stash -k -u Saved working directory and index state WIP on master: (...) (...) ```

In other parts of git, clumping (as defined by [GNU Short Option Style guide](https://www.gnu.org/software/tar/manual/html_node/Short-Options.html#SEC37)) works, for example:

-v for verbose, -m for message:
```
% git commit -vm 'xd'
[master a560195] xd
 1 file changed, 91 insertions(+), 51 deletions(-)
 rewrite spec/actions/hosting/meta_machine/upgrade_plan_spec.rb (96%)
```
-q for quiet, -m for message
```
% git commit -qm 'xd'
(no output)
```