Fix bugs that broke typedefs in function definitions.

Issue #118.

tests/typedef-3.ispc

@@ -0,0 +1,14 @@
+
+export uniform int width() { return programCount; }
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    typedef float Float[3];
+    float a = aFOO[programIndex];
+    Float x;
+    x[0] = 1;
+    x[1] = a;
+    x[2] = 2;
+    RET[programIndex] = x[b-4];
+}
+
+export void result(uniform float RET[]) { RET[programIndex] = 1+programIndex; }