Simplify cairo image surface creation and destruction

Simplify cairo image surface creation and destruction

* src/dispextern.h (struct image) [USE_CAIRO]: Remove member cr_data2.
* src/image.c (set_cairo_image_surface): New function split from
original create_cairo_image_surface.  Call cairo_surface_mark_dirty.
(create_cairo_image_surface): Just create image surface and return it.
(x_clear_image): Don't free cr_data2.
(xpm_load, pbm_load, png_load_body, jpeg_load_body, tiff_load)
(gif_load, imagemagick_load_image, svg_load_image) [USE_CAIRO]: Use
new create_cairo_image_surface and cairo_image_surface_get_data
instead of xmalloc.  Use set_cairo_image_surface instead of old
create_cairo_image_surface.
(pbm_load) [USE_CAIRO]: Call cairo_surface_destroy for surface instead
of xfree for data.
(gif_load) [USE_CAIRO]: Multiply y-coordinate value by width instead
of subimg_width.