RFR: rt-29185 Canvas won't Print.

[Phil Race]

http://cr.openjdk.java.net/~prr/fxprinting/rt-29185/

https://javafx-jira.kenai.com/browse/RT-29185

An exception was occurring because the Texture
resource backing the Canvas was not compatible with the 2D pipeline.

The fix adds code to Canvas to detect this case and copy the canvas data
to a compatible texture.

I tested this on Mac & Windows.

-phil.