create proofs folder, move proof-post-order utility to proofs directory, fix regression with proofs

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

src/ast/proofs/proof_utils.h

@@ -0,0 +1,42 @@
+/*++
+Copyright (c) 2017 Arie Gurfinkel
+
+Module Name:
+
+    proof_utils.h
+
+Abstract:
+    Utilities to traverse and manipulate proofs
+
+Author:
+    Bernhard Gleiss
+    Arie Gurfinkel
+
+Revision History:
+
+--*/
+
+#ifndef _PROOF_UTILS_H_
+#define _PROOF_UTILS_H_
+#include "ast/ast.h"
+
+/*
+ * iterator, which traverses the proof in depth-first post-order.
+ */
+
+class proof_post_order {
+public:
+    proof_post_order(proof* refutation, ast_manager& manager);
+    bool hasNext();
+    proof* next();
+
+private:
+    ptr_vector<proof> m_todo;
+    ast_mark          m_visited; // the proof nodes we have already visited
+    ast_manager&      m;
+};
+
+void reduce_hypotheses(proof_ref &pr);
+
+
+#endif