* app/Makefile.am
	* app/gimpdrawable-preview.[ch]: new files formerly known as
	gimpdrawablepreview.[ch].

	This is a new naming scheme for methods of objects which live
	outside their object's file. The old name implied a derived object
	(and is in fact now taken by a GimpPreview subclass, see below).

	Further candidates for renaming are e.g. gimpdrawable-invert.[ch],
	gimpimage-convert.[ch] etc.  Finaly, the main objects (image,
	drawable) will go to their own directories together with their
	subclasses.

	* app/apptypes.h: added typedefs for the new objects:

	* app/gimpbrushpreview.[ch]
	* app/gimppatternpreview.[ch]: new subclasses of GimpPreview.

	* app/gimpdrawablepreview.[ch]: contains a subclass of GimpPreview
	now.

	* app/gimpviewable.[ch]: renamed the virtual functions to
	"get_preview" and "get_new_preview" to avoid confusion with the
	new GimpPreview subclasses.

	* app/gimppreview.[ch]: virtualized "create_preview" and
	"create_popup".

	* app/gimpmarshal.[ch]: new marsaller for GimpPreview.

	* app/channels_dialog.c
	* app/fileops.c
	* app/gimpbrush.c
	* app/gimpdnd.c
	* app/gimpdrawable.c
	* app/gimpimage.c
	* app/gimppattern.c
	* app/layer_select.c
	* app/layers_dialog.c
	* app/lc_dialog.c
	* app/nav_window.c
	* app/palette_import.c
	* app/undo_history.c
	* app/pdb/drawable_cmds.c
	* app/pdb/image_cmds.c
	* tools/pdbgen/pdb/drawable.pdb
	* tools/pdbgen/pdb/image.pdb: changed accordingly.