added deep search of inheritance graph

test/set/post_old_error.cpp

@@ -0,0 +1,18 @@
+
+// Test post before old error (for free func, but same for all contracts).
+
+#include <boost/contract/function.hpp>
+#include <boost/contract/guard.hpp>
+
+void f() {
+    boost::contract::guard c = boost::contract::function()
+        .postcondition([] {}) // Error (post before old).
+        .old([] {})
+    ;
+}
+
+int main() {
+    f();
+    return 0;
+}
+