Update `trunk/Manuals/Docbook' directory structure:
    
        - Keep both preamble and parts in just one file
          (`repository.docbook'). Indeed, it is advisable to have just one
          `.docbook' file in this location in order for `locales'
          functionality to use. Otherwise, if more than one .docbook file
          is found by `locale' functionality, they would be used to
          retrive translatable strings too, and we don't need that becuase
          entities inside .docbook files are expanded before retriving
          translatable strings. This way, only one `.docbook' files is
          needed in this location (i.e., the main document structure
          definition file [e.g., `repository.docbook']).