Preprocessor update

– gracefully error out when a PAC model is not used in a pac_expectation
  operator
– fix handling of model local variable in DataTree copy constructor

preprocessor @ 7f22b38a

-Subproject commit 5da05127ca47c7221d5f047a497f6ec8e5c6ce16
+Subproject commit 7f22b38a230c3ad1afc76e1c796adccdf4f2538d