additional robustness check for incremental sat solver core when it recieves interpreted constants, added PB equality to interface and special handling of equalities to adddress performance gap documented in #755

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/solver/combined_solver.cpp

@@ -196,6 +196,7 @@ public:
 
     virtual lbool get_consequences(expr_ref_vector const& asms, expr_ref_vector const& vars, expr_ref_vector& consequences) {
         switch_inc_mode();
+        m_use_solver1_results = false;
         return m_solver2->get_consequences(asms, vars, consequences);
     }