If inside a for-loop, sampler array index is the loop index, Mac cg compiler will crash.  This CL unroll the loop in such situation.  The behavior is:
1) If the for-loop index is a float, we reject the shader.
2) If it is an integer, we unroll the for-loop.

Things that should be done in the future are:
1) Add line number macros.
2) Add a limit to unroll iteration count.

anglebug=94
Review URL: http://codereview.appspot.com/4331048

git-svn-id: https://angleproject.googlecode.com/svn/trunk@606 736b8ea6-26fd-11df-bfd4-992fa37f6226