reorganizing the code

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/tactic/nlsat/nlsat_tactic.cpp

@@ -232,6 +232,7 @@ public:
             throw ex;
         }
         catch (z3_exception & ex) {
+            // convert all Z3 exceptions into tactic exceptions.
             throw tactic_exception(ex.msg());
         }
     }