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/option.hh
--- src/option.hh.orig
+++ src/option.hh
@@ -22,9 +22,9 @@
 #include <stdexcept>
 #include <map>
 #include <set>
-#include "vector.hh"
-
 #include <boost/function.hpp>
+
+#include "vector.hh"
 #include "lexical_cast.hh"
 
 #include "sanity.hh"