Fixed == operator for empty string comparison.

ZString.h

@@ -311,13 +311,13 @@ namespace coreutils {
       /// the number of bytes specified by size.
       ///
       
-      char *getData();
+      char *getData() const;
       
       ///
       ///
       ///
       
-      char *getCursor();
+      char *getCursor() const;
       
       ///
       ///
@@ -329,7 +329,7 @@ namespace coreutils {
       /// Return the length of the ZString.
       ///
       
-      size_t getLength();
+      size_t getLength() const;
       
       ///
       /// Set this ZString to have the same data space as the ZString pointer