Add test for the bug in issue #204.

tests/ref-vec-param-index.ispc

@@ -0,0 +1,16 @@
+
+export uniform int width() { return programCount; }
+
+float foo(uniform float<4> &vec) {
+    return vec[programIndex & 3];
+}
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    uniform float<4> vec = { b, -1, 2*b, -b };
+    RET[programIndex] = foo(vec); 
+}
+
+export void result(uniform float RET[]) {
+    uniform float a[4] = { 5, -1, 10, -5 };
+    RET[programIndex] = a[programIndex & 3];
+}