Test case and fix for shlex.split unicode bug

When operating on a unicode string in python 2.6, shlex.split returns
a result that does not work with the file constructor.

This causes task includes to fail because python cannot open the included task.

To reproduce this requires a task include that is templated (this is
because the templated string is a unicode result, whereas a non-
templated string is a non-unicode string)
```
[will@centos6.3] $ python
Python 2.6.6 (r266:84292, Sep 11 2012, 08:34:23)
[GCC 4.4.6 20120305 (Red Hat 4.4.6-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import shlex
>>> shlex.split(u'abc')
['a\x00\x00\x00b\x00\x00\x00c\x00\x00\x00']

[will@fedora17] $ python
Python 2.7.3 (default, Jul 24 2012, 10:05:38)
[GCC 4.7.0 20120507 (Red Hat 4.7.0-5)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import shlex
>>> shlex.split(u'abc')
['abc']
```
The proposed fix (coercing the include parameters to string before the
shlex.split) may not be ideal but it does fix the bug for my test case.