get_location
Description:
Find the real folder (and message info UID) for the given vinfo.
 When the realuid is not null and it's set, then use 
      g_free to free it, when no longer needed.
Parameters:
| this | |
| vinfo | a VeeMessageInfo to search for | 
| realuid | if not null, set to the UID of the real message info | 
Returns:
| a real (not virtual) Folder, which the  |