Added >= and <= operators to ZString.

ZString.cpp

@@ -80,6 +80,16 @@ namespace coreutils {
       return 0;          
    }
 
+   // TODO: Fix the following comparison operators to handle the length problem appropriately.
+   
+   bool ZString::operator<=(const ZString &valuex) const {
+      return (strncmp(data, valuex.data, valuex.length <= length ? valuex.length : length) <= 0);
+   }
+   
+   bool ZString::operator>=(const ZString &valuex) const {
+      return (strncmp(data, valuex.data, valuex.length <= length ? valuex.length : length) >= 0);
+   }
+   
    bool ZString::operator>(const ZString &valuex) const {
       return (strncmp(data, valuex.data, valuex.length <= length ? valuex.length : length) > 0);
    }