Supporting untracked files with `git pull --autostash`

[mqudsi@neosmart.net]

Hello,

Just a quick request for an enhancement to the behavior of the following
command:

    git pull --autostash --rebase

When executed with local, untracked files that would conflict with newly-added
files upstream, e.g.

An untracked local file `master:/foo` would be overwritten by a recently tracked
file `origin/master:/foo`.

Currently, the following occurs:

```
mqudsi@devpc > git pull --autostash --rebase
First, rewinding head to replay your work on top of it...
error: The following untracked working tree files would be overwritten by
checkout:
        tests/eval.err
		tests/eval.in
		tests/eval.out
```

where

```
mqudsi@devpc > git status --porcelain=v2 | grep eval
? tests/eval.err
? tests/eval.in
? tests/eval.out
```

As currently `--autostash` only applies to files that are tracked by git, and
files not in the index are ignored.

(Additionally, with this change it makes sense to enable `--autostash` to be used
with a plain `git pull` without necessary also including `--rebase`, but I can
live without it!)

Thank you,

Mahmoud Al-Qudsi
NeoSmart Technologies