[cairo] Tessellator performance patch

[chris nuernberger]

Now we both might be daft for sure, but if I understand you then it
should boil down to two if statements, as if the x order of the ends
of the segments switches.

I honestly was wondering the same thing, it is suggested on at least
one web page on b-o.  But unlike you I didn't have the courage to ask
to the entire list, or the time to figure out the code...