[BZ#338385] Support of SVG 1.2 "comp-op" property
Submitted by Emmanuel Pacaud
It's a feature used in current cairo SVG backend for support of cairo operators without using image fallbacks.
Following operations are used:
clear, src, src-over, src-in, src-out, src-atop, dst, dst-over, dst-in, dst-out, dst-atop, xor, plus, color-dodge
I'm not sure about color-dodge, which would be used for CAIRO_OPERATOR_SATURATE.