Add option to ignore files following a pattern.

Useful for when using SVN and we have both fixtures/media and MEDIA_ROOT checked in i.e.:

- *someapp/fixtures/media/.svn*
- *var/media/.svn* (MEDIA_ROOT)

We want to preserve the .svn directory at MEDIA_ROOT and not overwrite it with the one at *someapp/fixtures/media/.svn*. This produces the adverse effect of having switched a branch.