Paths: add new SwitchRoot method
Paths: add new SwitchRoot method

This method will be used to switch the mount point of a path with a
different one. Example:

 SwitchRoot ("/foo/bar/", "/foo", "/baz") == "/baz/bar"

First usage of it will be in Banshee, in an upcoming
patch for N95 playlists support (bgo#661507).

arfbtwn/hyena,GNOME/hyena,arfbtwn/hyena,GNOME/hyena