[PATCH 0 of 1 RFC] Fix handling of shell alias arguments

[Steve Losh]

I'm not sure if this patch got through the last time I sent it -- it didn't
show up in my inbox, so I'm sorry if this is a duplicate.

This patch attempts to change how arguments to shell aliases are parsed to
make them work the way people probably expect.

In a nutshell, without this patch the following will fail:

    [alias]
    own = !chown $@ `$HG root`

    $ hg own -R sjl

With this patch it will work as expected.

The code could probably be cleaned up a bit, but I wanted to get some opinions
on the approach/result first.

I'd like to get this in for 1.7, because once shell aliases are in an official
release it will be much more painful to change their behavior.

The patch's commit message has more information.