move qhead to attribute on the state instead of the simplifier,

- add sat.smt option to enable the new incremental core (it is not ready for mainstream consumption as cloning and other features are not implemented and it hasn't been tested in any detail yet).
- move "name" into attribute on simplifier so it can be reused for diagnostics by the seq-simplifier.

src/ast/simplifiers/dependent_expr_state.h

@@ -41,6 +41,7 @@ Author:
    abstract interface to state updated by simplifiers.
  */
 class dependent_expr_state {
+    unsigned m_qhead = 0;
 public:
     virtual ~dependent_expr_state() {}
     virtual unsigned size() const = 0;
@@ -53,8 +54,15 @@ public:
     trail_stack    m_trail;
     void push() { m_trail.push_scope(); }
     void pop(unsigned n) { m_trail.pop_scope(n); }
-
-
+    unsigned qhead() const { return m_qhead; }
+    void advance_qhead() { m_qhead = size(); }
+    unsigned num_exprs() {
+        expr_fast_mark1 visited;
+        unsigned r = 0;
+        for (unsigned i = 0; i < size(); i++) 
+            r += get_num_exprs((*this)[i].fml(), visited);
+        return r;
+    }
 };
 
 /**
@@ -65,14 +73,13 @@ protected:
     ast_manager& m;
     dependent_expr_state& m_fmls;
     trail_stack& m_trail;
-    unsigned              m_qhead = 0;          // pointer into last processed formula in m_fmls
 
     unsigned num_scopes() const { return m_trail.get_num_scopes(); }
 
-    void advance_qhead() { if (num_scopes() > 0) m_trail.push(value_trail(m_qhead)); m_qhead = m_fmls.size(); }
 public:
     dependent_expr_simplifier(ast_manager& m, dependent_expr_state& s) : m(m), m_fmls(s), m_trail(s.m_trail) {}
     virtual ~dependent_expr_simplifier() {}
+    virtual char const* name() const = 0;
     virtual void push() { }
     virtual void pop(unsigned n) { }
     virtual void reduce() = 0;
@@ -80,7 +87,8 @@ public:
     virtual void reset_statistics() {}
     virtual void updt_params(params_ref const& p) {}
     virtual void collect_param_descrs(param_descrs& r) {}
-    unsigned qhead() const { return m_qhead; }
+    ast_manager& get_manager() { return m; }
+    dependent_expr_state& get_fmls() { return m_fmls; }
 };
 
 /**