actually) to a png file.

	* bin/Makefile.am: added export.[ch], link with libpng.
	* bin/export.[ch] NEW: a dialog to handle exporting parts/all fo the
	defined region.
	* bin/editor.c: (cb_export): added export menu entry/shortcut.
	* bin/editor.h:
	* bin/gegl-projection.[ch]: (task_render), (task_monitor),
	(gegl_projection_render), (gegl_projection_get_buffer):
	* bin/gegl-view.c: (gegl_view_get_projection):
	* bin/gegl-view.h: