- don't include <gdk-pixbuf/gdk-pixbuf.h> in headers in app/
- instead, include it in many .c files instead of <glib-object.h>,
finally acknowledging the fact that app/ depends on gdk-pixbuf almost
globally
- fix up includes as if libgimpbase depended in GIO, which it soon will
The new by-row iteration doesn't re-write the length
value for each row. In general it is not safe to modify
the iterator data because the internal logic depends
on the public data, but this specific case is new.
