Add stipple support on cairo

Add stipple support on cairo

* src/xterm.h (struct x_bitmap_record) [USE_CAIRO]: Remove unused member img.
Add member stipple.
(x_bitmap_stipple) [USE_CAIRO]: Add extern.

* src/image.c (x_bitmap_stipple) [HAVE_X_WINDOWS && USE_CAIRO]: New function.
(image_create_bitmap_from_data, image_create_bitmap_from_file)
(x_create_bitmap_from_xpm_data) [HAVE_X_WINDOWS && USE_CAIRO]: Initialize
stipple member of struct x_bitmap_record.
(free_bitmap_record) [HAVE_X_WINDOWS && USE_CAIRO]: Destroy stipple member.

* src/xterm.c (x_fill_rectangle) [USE_CAIRO]: Inspect gc and draw stipple if
necessary.  Use x_bitmap_stipple.