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/vocab.cc
--- src/vocab.cc.orig
+++ src/vocab.cc
@@ -11,8 +11,8 @@
 #include "base.hh"
 #include "constants.hh"
 #include "hash_map.hh"
-#include "sanity.hh"
 #include "vocab.hh"
+#include "sanity.hh"
 #include "char_classifiers.hh"
 #include "transforms.hh"