This is technically an API break, as the following assignment may now
raise warnings in user code:
```
gchar *filename = g_osx_app_info_get_filename (app_info);
```
However, from code search it seems like the number of users of that
function is zero.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
This is an implementation of most of GAppInfo using the OS X
NSBundle APIs.
Missing at this point are things that don't have equivalents
in OS X, such as hidden desktop files, last-used, manual type
associations, and g_app_info_get_all().
https://bugzilla.gnome.org/show_bug.cgi?id=734946