Fixed construct_asset_path for windows

in windows css_path will contain backslashes so using posixpath.dirname will
not work properly. 
need to use os.path.dirname and then convert to posix

Add -p argument to the CoffeeScript compiler

provide required argument

````
class BaseStorageFinder(BaseFinder):

    ...

    def list(self, ignore_patterns):
        
       ....
````

this class is present (and identical with regards to the list method) in both : 

````
staticfiles/finders.py @215
django/contrib/staticfiles/finders.py @206
````

Some kind of argument needs to be provided. this change prevents a yellow error screen.

fix jinja2 tests

Signed-off-by: Timothée Peignier <timothee.peignier@tryphon.org>

* When the target file doesn't exist, it counts as "outdated"

* url rewriting outputs unicode, so expect unicode

* re.sub needs to take a unicode string, not a byte string

add support for slimit compressor

fix an IOError