Fixed MString and MFile.

testing/mfile_test.cpp

@@ -0,0 +1,7 @@
+#include <iostream>
+#include "../MFile.h"
+int main(int argc, char **argv) {
+   coreutils::MFile data("testdata.data");
+   std::cout << data << std::endl;
+   return 0;
+}