8.0-graphics-scrum-1527: up to 20% performance regression in Guimark2.Vector and Charts.Stock benchmarks on Win7-High

There are following regressions first appeared in 8.0-graphics-scrum-1527 and 8.0-controls-scrum-715.
 -21% (-6.03 fps) in Charts.Stock
 -17% (-7.86 fps) in GUIMark2.Vector


Unfortunately, there are no 8.0-graphics-scrum-152[3-6] and 8.0-controls-scrum-714 builds available
and both 8.0-graphics-scrum-1527 and 8.0-controls-scrum-715 contains merges with MASTER. So, it is not
quite obvious which scrum introduced the regression.

According to JPA profiles for Guimark2.Vector the time spent in
com.sun.prism.impl.shape.NativePiscesRasterizer.produceStrokeAlphas and produceFillAlphas
has been increased correspondingly.

The issue is not visible on WinXP-mid-range, but I can reproduce it on Dell laptopn with Intel graphics.

Steps to reproduce the issue (please, run on Windows):
> cd JFX_WS/tests/performance/GUIMark2
> ant
> java -Djavafx.animation.fullspeed=true
       -cp "JFX_HOME/rt/lib/ext/jfxrt.jar:./dist/GUIMark2.jar:../FXBenchmark/dist/FXBenchmark.jar:../../../import/benchmarks-2.1.1/benchmarks-2.1.1.jar"
 jrockit.bm.Main guimark2.bm.VectorBenchmark -i 1 -wt 5 -tr 30