* app/core/gimpdrawable.[ch]: add "gboolean push_undo" to
GimpDrawable::convert_type().
* app/core/gimpdrawable-convert.[ch]: same here for the gray and rgb
conversion functions.
* app/core/gimpchannel.c
* app/core/gimplayer.c: pass FALSE when called from GimpItem::convert()
because it can be called on unattached items only.
* app/core/gimpimage-convert.c: pass TRUE.
* app/core/core-enums.[ch]
* app/core/gimpgrouplayerundo.[ch]
* app/core/gimpimage-undo-push.[ch]: add GIMP_UNDO_GROUP_LAYER_CONVERT
which simply calls gimp_drawable_convert_type() with the old type
when undone/redone.
* app/core/gimpgrouplayer.c: push a group layer convert undo so this
can be properly undone/redone.
* app/core/gimpgrouplayer.[ch]: add gimp_group_layer_suspend_resize()
and gimp_group_layer_resume_resize() and call them around functions
where all a group's children are transformed (translated, resized
etc). This way we go from the worst case of reallocating the
group's projection tiles once for each child down to exactly one
reallocation.
* app/core/Makefile.am
* app/core/core-enums.[ch]
* app/core/core-types.h
* app/core/gimpimage-undo-push.[ch]
* app/core/gimpgrouplayerundo.[ch]: add new undo class
GimpGroupLayerUndo which implements undos for suspend/resume of
group layers and calls them in reverse order when undoing.
