Fix some memory leaks.

* src/named-ref.c: Add a pointer check (named_ref_free).
	* src/scan-code.l: New function (variant_table_free). Called in
	code_scanner_free.
	* src/symlist.c: Call to named_ref_free (symbol_list_free).

src/named-ref.c

@@ -36,6 +36,7 @@ named_ref_new (uniqstr id, location loc)
 void
 named_ref_free (named_ref *r)
 {
-  free (r);
+  if (r)
+    free (r);
 }