[cairo] Drawing into a memory block

[Jonathan Roewen]

Results of make check.

PASS: fill_rule
PASS: leaky_polygon
PASS: line_width
PASS: linear_gradient
XFAIL: move_to_show_surface
FAIL: text_cache_crash
XFAIL: text_rotate
FAIL: coverage
PASS: clip_twice
XFAIL: pixman_rotate
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2 of 10 tests failed
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> Have you run "make check"? It runs several tests, most of which draw
> using the image backend, so it would be good to start with that to
> make sure it is working properly.