update for lib/utils split

Update sources with the new paths

lib/mu-msg-file.c

@@ -28,12 +28,13 @@
 #include <inttypes.h>
 
 #include <gmime/gmime.h>
-#include "mu-util.h"
-#include "mu-str.h"
 #include "mu-maildir.h"
 #include "mu-store.hh"
 #include "mu-msg-priv.h"
 
+#include "utils/mu-util.h"
+#include "utils/mu-str.h"
+
 static gboolean init_file_metadata (MuMsgFile *self, const char* path,
 				    const char *mdir, GError **err);
 static gboolean init_mime_msg (MuMsgFile *msg, const char *path, GError **err);