[OpenJDK 2D-Dev] RFR: 8204391: Colors with alpha are painted incorrectly on Linux

[Phil Race]

Bug: https://bugs.openjdk.java.net/browse/JDK-8204931
Webrev: http://cr.openjdk.java.net/~prr/8204931/

There is a long evaluation in the bug report, so what I write here is 
just a summary.

This is a regression introduced by 
https://bugs.openjdk.java.net/browse/JDK-8176795
and specific to the Xrender pipeline

The bug is that when using colors with alpha, the alpha is being ignored 
and the colour
copied rather than blended, since we no longer pass the "pre-multiplied" 
flag as false.

The fix is to pre-multiply the colour when storing as a pixel even for 
an opaque xrender surface.

With this fix automated jtreg tests, and tck tests pass, as well as the 
manual TCK test that was failing.

Additionally the supplied regression test passes on all platforms.

-phil