File name repository.
  This class stores file names and can check whether a file has been 
  modified or not since a previous call. A file name is stored by calling 
  acquire_filename() which returns an ID and a signature of the file. The 
  signature can later be used to check if the file was modified by calling 
  is_file_modified(). If the file name is no longer required 
  release_filename() should be called so that the entry can be removed from
  the repository.
    |  |  | 
    |  | 
        
          | acquire_filename(self,
        name) Acquire a file name and return its id and its signature.
 | source code |  | 
    |  | 
        
          | release_filename(self,
        id_) Release a file name.
 | source code |  | 
    |  | 
        
          | is_file_modified(self,
        id_,
        signature) Check if the file referred to by id_ has been modified.
 | source code |  | 
    |  | 
        
          | update_id_counter(self) Update the id_ counter so that it doesn't grow forever.
 | source code |  |