Added assignment to MString from ZString operator=.

MString.h

@@ -94,11 +94,10 @@ namespace coreutils
       ///
       /// Assignment operator will copy data to backing store.
       ///
-      
-      //      MString& operator=(coreutils::ZString& data);
-      
+            
       MString &operator=(coreutils::MString data);
-      
+      MString &operator=(coreutils::ZString data);
+
       ///
       /// Assignment operator will copy data to backing store.
       ///