Fix bugs that broke typedefs in function definitions.

Issue #118.

tests/typedef-4.ispc

@@ -0,0 +1,10 @@
+
+export uniform int width() { return programCount; }
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    typedef float Float;
+    Float a = aFOO[programIndex];
+    RET[programIndex] = a;
+}
+
+export void result(uniform float RET[]) { RET[programIndex] = 1+programIndex; }