Add tests for function pointers.

tests/funcptr-uniform-10.ispc

@@ -0,0 +1,25 @@
+
+export uniform int width() { return programCount; }
+
+typedef float (*FuncType)(float, float);
+
+float foo(float a, float b) {
+    return a+b;
+}
+
+static float bar(float a, float b) {
+    return min(a, b);
+}
+
+
+export void f_f(uniform float RET[], uniform float aFOO[]) {
+    uniform FuncType func[] = { bar, foo };
+    float a = aFOO[programIndex]; 
+    float b = aFOO[0]-1; // == 0
+    func[min(a, 0)] = foo;
+    RET[programIndex] = func[0](a, b);
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = programIndex+1;
+}