Add a test for the compare opcode.

This is a test for the compare opcode (CMP).  This should draw a green triangle
in the fs-test.

src/gallium/tests/python/tests/regress/fragment-shader/frag-cmp.sh

@@ -0,0 +1,12 @@
+FRAG
+
+DCL IN[0], COLOR, LINEAR
+DCL OUT[0], COLOR
+
+IMM FLT32 { 1, 0, 0, 1 }
+IMM FLT32 { 0, 1, 1, 0 }
+IMM FLT32 { 1, 0,-1, 0 }
+
+CMP OUT[0], IMM[2], IMM[0], IMM[1]
+
+END