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/enumerator.cc
--- src/enumerator.cc.orig
+++ src/enumerator.cc
@@ -11,9 +11,9 @@
 #include <deque>
 #include <map>
 #include <set>
-#include "vector.hh"
 
 #include "cset.hh"
+#include "vector.hh"
 #include "enumerator.hh"
 #include "revision.hh"
 #include "vocab.hh"