Fixed == operator for empty string comparison.

MString.cpp

@@ -38,12 +38,18 @@ namespace coreutils {
       cursor = this->data;
    }
 
-   MString::MString(ZString zstring) {
+   MString::MString(const ZString &zstring) {
       setSize(zstring.getLength());
       memcpy(data, zstring.getData(), zstring.getLength());
       cursor = data;      
    }   
-   
+
+   MString::MString(ZString &zstring) {
+      setSize(zstring.getLength());
+      memcpy(data, zstring.getData(), zstring.getLength());
+      cursor = data;
+   }
+  
    MString::MString(const MString &mstring) {
       setSize(mstring.length);
       memcpy(data, mstring.data, mstring.length);