set_file
Description:
Sets the `GtkMediaFile` to play the given file.
If any file is still playing, stop playing it.
Parameters:
| this | 
           a `GtkMediaFile`  | 
      
| file | 
           the file to play  | 
      
Sets the `GtkMediaFile` to play the given file.
If any file is still playing, stop playing it.
| this | 
           a `GtkMediaFile`  | 
      
| file | 
           the file to play  |