Issue error if "typedef" is inadvertently included in function definition.

Issue #267.

parse.yy

@@ -1862,6 +1862,8 @@ function_definition
             const FunctionType *funcType = CastType<FunctionType>($2->type);
             if (funcType == NULL)
                 AssertPos(@1, m->errorCount > 0);
+            else if ($1->storageClass == SC_TYPEDEF)
+                Error(@1, "Illegal \"typedef\" provided with function definition.");
             else {
                 Stmt *code = $4;
                 if (code == NULL) code = new StmtList(@4);

tests_errors/func-def-with-typedef.ispc

@@ -0,0 +1,4 @@
+// Illegal "typedef" provided with function definition
+
+typedef float foo(float a, float b) { }
+