Replace includes of boost/filesystem.h with fs.h

This is step one in abstracting the use of boost::filesystem.

src/rpc/server.cpp

@@ -6,6 +6,7 @@
 #include "rpc/server.h"
 
 #include "base58.h"
+#include "fs.h"
 #include "init.h"
 #include "random.h"
 #include "sync.h"
@@ -16,7 +17,6 @@
 #include <univalue.h>
 
 #include <boost/bind.hpp>
-#include <boost/filesystem.hpp>
 #include <boost/foreach.hpp>
 #include <boost/shared_ptr.hpp>
 #include <boost/signals2/signal.hpp>