[cairo] Tiny SVG performance improvement

[Steve Snyder]

Hello, all.

I submitted this to Mozilla, and it was suggested that I report it here as 
well:  https://bugzilla.mozilla.org/show_bug.cgi?id=368408

I looked at FreeDesktop's Bugzilla form and realized I don't know enough 
about Cairo and it's versions & subsystems to make a non-stupid bug 
submittal.  Hence the bare link above.

Side note: Readers not familiar /w Mozilla code might wonder about that 
"even with the MMX re-enabled" comment.  The MMX support in pixman was 
thought to be the cause of a bug and so was disabled in the Mozilla 
builds.  It was later discovered that the MMX was not to blame, but the 
MMX code was never re-enabled.

FYI.