Preserve filename when closing a file

[ghost]

Minor update to behave like django's own FileSystemStorage when closing a dirty file pointer.

[andres-torres-marroquin]

Hey, could you add some tests for this? Thanks!

[ghost]

Hello, my original intention was to pull only 7b3ec3d, I added the cache thing later. If you want to keep it I can create some tests (I use it in yawd-elfinder anyway because RESTfull APIs are slow). If you don't need the caching I can create a new pull request with the fp fix alone.

[andres-torres-marroquin]

Sounds good, thanks!