A function macro named E clashes with internal boost definitions.  Rearrange
the order of header inclusion so that affected boost headers are included
before monotone defines the macro.

Also, stop bundling boost/circular_buffer, which is available in current
versions of boost. From Fedora.

Index: src/hmac.cc
--- src/hmac.cc.orig
+++ src/hmac.cc
@@ -10,9 +10,9 @@
 #include "base.hh"
 #include <botan/botan.h>
 
-#include "sanity.hh"
 #include "hmac.hh"
 #include "vocab.hh"
+#include "sanity.hh"
 #include "constants.hh"
 
 using std::string;