Many fixes for MString, ZString.

File.h

@@ -24,7 +24,7 @@ namespace coreutils {
       void write(std::string data);
       void write(coreutils::ZString &data);
       std::string asString();
-
+      coreutils::ZString& asZString();
       char *buffer;
       size_t size;
 
@@ -33,6 +33,7 @@ namespace coreutils {
     private:
       void open(std::string fileName, int mode, int authority);
       int fd;
+      coreutils::ZString zstring;
 
    };