get-directory in Dialogs

• (get-directory message parent directory style) -> string or #f
   message = #f : string or #f
   parent = #f : frame% or dialog% object or #f
   directory = #f : string or #f
   style = null : list of symbols in '(enter-packages)

  Obtains a directory pathname from the user via the platform-specific standard (modal) dialog, using parent as the parent window if it is specified.

  If directory is not #f, it is used on some platforms as the starting directory for the directory selector (otherwise the starting directory is chosen automatically in a platform-specific manner, usually based on the current directory and the user's interactions in previous calls to get-file, put-file, etc.).

  The style argument is either the empty list or the list containing the single item 'enter-packages. The difference matters only under Mac OS, where 'enter-packages enables the user to select package directory or a directory within a package. A package is a directory with a special suffix (e.g., ``.app'') that the Finder normally displays like a file.