implemented [trusted] attribute for the ml prover
implemented basic AC-unification for BuiltinSet
evaluated the LHS of a rule as well
minor cleanup
Revert "evaluated the LHS of a rule as well"

This reverts commit e3dca7885d4b3e9927597dd6c55567d709c9223d.
added comment
Merge pull request #1137 from yilongli/prove-cil-list-reverse-2

patch in order to prove the entire cil list reverse example