Allow future keywords to be accessed as members in a struct.

This fixes a bug where a token that could be a keyword in one version
is not a keyword in another version, but treated like a non-member after
a "." dereference.

Test/330.frag

@@ -140,3 +140,11 @@ void qlod()
     lod = textureQueryLod(samp1D, pf);      // ERROR, not until 400
     lod = textureQueryLod(samp2Ds, pf2);    // ERROR, not until 400
 }
+
+int precise;                // okay, not a keyword yet
+struct SKeyMem { int precise; } KeyMem; // okay, not a keyword yet
+
+void fooKeyMem()
+{
+    KeyMem.precise;
+}