Fixed gl_FragCoord emulation for point sprites of size > 1 using VPOS semantic for x and y coordinates rather than previous per-vertex emulation when running on Shader Model 3.
Fixed gl_FragCoord emulation for point sprites of size > 1 using VPOS
semantic for x and y coordinates rather than previous per-vertex
emulation when running on Shader Model 3.

Verified fix in Chromium with test case from bug.

BUG=http://code.google.com/p/angleproject/issues/detail?id=71
TEST=test case from bug
TBR=nicolas (LGTM'd by dgkoch)

Review URL: http://codereview.appspot.com/2921041

csulmone/angle,csulmone/angle,csulmone/angle,csulmone/angle