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

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

src/wallet/wallet.cpp

@@ -11,6 +11,7 @@
 #include "wallet/coincontrol.h"
 #include "consensus/consensus.h"
 #include "consensus/validation.h"
+#include "fs.h"
 #include "key.h"
 #include "keystore.h"
 #include "validation.h"
@@ -30,7 +31,6 @@
 #include <assert.h>
 
 #include <boost/algorithm/string/replace.hpp>
-#include <boost/filesystem.hpp>
 #include <boost/thread.hpp>
 
 CWallet* pwalletMain = NULL;