convert reduce-args to a simplifier

- convert reduce-args to a simplifier. Currently exposed as reduce-args2 tactic until the old tactic code gets removed.
- bug fixes in model_reconstruction trail
  - allow multiple defs to be added with same pool of removed formulas
  - fix tracking of function symbols instead of expressions to filter replay
- add nla_divisions to track (cheap) divisibility lemmas.
-

src/math/lp/nla_divisions.h

@@ -0,0 +1,31 @@
+/*++
+Copyright (c) 2017 Microsoft Corporation
+
+Module Name:
+
+  nla_divisions.h
+
+Author:
+  Lev Nachmanson (levnach)
+  Nikolaj Bjorner (nbjorner)
+
+Description:
+  Check division constraints.
+  
+--*/
+
+#include "math/lp/nla_types.h"
+
+namespace nla {
+    
+    class core;
+    
+    class divisions {
+        core& m_core;
+        vector<std::tuple<lpvar, lpvar, lpvar>> m_idivisions;
+    public:
+        divisions(core& c):m_core(c) {}
+        void add_idivision(lpvar r, lpvar x, lpvar y);
+        void check(vector<lemma>&);
+    };
+}