Change the DatalogGuard to compute the max prin.
Change the DatalogGuard to compute the max prin.

This commit changes the DatalogGuard to use the max principal length in
a query to bound the search space of (Var, Const, Const) productions
Datalog. This allows us to simplify datalog rules by writing things like
forall X: forall Y: forall Z: A(X) and B(Y) and Subprin(Z, X, Y) implies
A(Z).

cjpatton/cloudproxy,William-J-Earl/cloudproxy,William-J-Earl/cloudproxy,tmroeder/cloudproxy,jlmucb/cloudproxy,jlmucb/cloudproxy,William-J-Earl/cloudproxy,jethrogb/cloudproxy,kevinawalsh/cloudproxy,jlmucb/cloudproxy,jlmucb/cloudproxy,jlmucb/cloudproxy,kevinawalsh/cloudproxy,tmroeder/cloudproxy,tmroeder/cloudproxy,William-J-Earl/cloudproxy,jethrogb/cloudproxy,cjpatton/cloudproxy,cjpatton/cloudproxy,jethrogb/cloudproxy,tmroeder/cloudproxy,jethrogb/cloudproxy,tmroeder/cloudproxy,jethrogb/cloudproxy,cjpatton/cloudproxy,cjpatton/cloudproxy,William-J-Earl/cloudproxy