* app/paint/gimppaintcore.[ch]: add
  gimp_paint_core_{get|set}_{current|last}_coords(), add "const GimpCoords*"
  parameter to ::paint() which gets core->cur_coords passed.

* app/paint/gimpsourcecore.[ch]: add "const GimpCoords*" to ::motion().

* app/paint/gimpbrushcore.c: use the new coords getters/setters instead
  of accessing GimpPaintCore members directly.

* app/paint/gimpairbrush.c
* app/paint/gimpclone.c
* app/paint/gimpconvolve.c
* app/paint/gimpdodgeburn.c
* app/paint/gimperaser.c
* app/paint/gimpheal.c
* app/paint/gimpink.c
* app/paint/gimppaintbrush.[ch]
* app/paint/gimpperspectiveclone.c
* app/paint/gimpsmudge.c: change implementations of GimpPaintCore::paint()
  and GimpSourceCore::motion() accordingly. app/paint/ is now virtually
  free of direct access to the paint core's coords members. More to come...