[DROOLS-50] fix combined use of memberOf and null safe dereferencing
(cherry picked from commit ef4dc900927df4c5d6b444e51224bebe56670256)
[DROOLS-51] fix positional constraint when using a null as value
[DROOLS-54] fix QueryElement.clone by cloning also the contained pattern
[DROOLS-61] generate a proper compilation failure when trying to use non-public classes in drl
(cherry picked from commit ca31c2fb77762170f154642aefdd13d239d31b52)