Further reduce header dependencies

This commit removes the dependency of serialize.h on PROTOCOL_VERSION,
and makes this parameter required instead of implicit. This is much saner,
as it makes the places where changing a version number can have an
influence obvious.

src/qt/qtipcserver.cpp

@@ -7,6 +7,7 @@
 #include <boost/tokenizer.hpp>
 #include <boost/date_time/posix_time/posix_time.hpp>
 
+#include "ui_interface.h"
 #include "util.h"
 #include "qtipcserver.h"