gfx: polygon: optimize a bit
gfx: polygon: optimize a bit

* use qsort() for a large number of intersections
* call hline directly from the code that computes scanlines

Signed-off-by: Cyril Hrubis <b1e90efd3b808b8e0bcf2a9a55fd8b9a779bfd81@ucw.cz>

gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim