string: add indirection operator for tokeniser::iterator

string.hpp

@@ -83,6 +83,11 @@ namespace util {
                 return m_range;
             }
 
+            const range_type* operator-> (void) const
+            {
+                return &m_range;
+            }
+
             bool operator== (const iterator &rhs) const
             {
                 return m_range == rhs.m_range && m_separator == rhs.m_separator;