Allow GIO to open non-file:// URIs
The GIO backend should be able to handle many different kinds of filesystem types. Currently the implementation only supports file:// URIs. This is a set of changes to take advantage of the ability to handle any other URL that the GIO GVFS supports.
The only part I'm not 100% happy with is the workaround for python issue 18828 with smb:// urls, but it seems like there's not a lot of great options in the standard library.