[cairo] Image fallback in PS backend

[Behdad Esfahbod]

Hi,

Just wondering:  I see there are checks in the PS backend to
short-circuit clear operations when we have not started a new
page yet...  One can improve the analyze surface a bit, to allow
OVER operations with transparency on a new page, even when the
backend (PS) does not support transparent OVER.  This way we
should get decent output for the minefield with PS backend, as
the image is in the background and will be drawn before anything
else, or that's what I assume :).

--behdad
http://behdad.org/

"Commandment Three says Do Not Kill, Amendment Two says Blood Will Spill"
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