Added the ability to run external files in the context of qtile

Example:
In an external editor, I write code for qtile and I want to test it without restarting qtile.
For example in the file /tmp/test.py I write:
```python
def main (qtile):
     print qtile.currentLayout
     qtile.cmd_nextlayout ()
     print qtile.currentLayout
```
then run: qsh -r /tmp/test.py
and get to stdout:
```shell
<libqtile.layout.xmonad.MonadTall object at 0x7fc06a964c50>
<libqtile.layout.max.Max object at 0x7fc06a964bd0>
```
On Sun, Aug 31, 2014 at 06:50:17AM -0700, Vladimir wrote:
> > @@ -1,17 +1,17 @@
> > -#!/usr/bin/env python
> > +#!/usr/bin/env python2
> 
> Well, what should I do? Send a new PR without this line?

Ah, I think if you push another commit to this branch on github it
should show up in this PR so you don't have to open a whole new one.

> ---
> Reply to this email directly or view it on GitHub:
> https://github.com/qtile/qtile/pull/488/files#r16934959