Fix compiler problem with newer gcc.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4281 dfc29bdd-3216-0410-991c-e03cc46cb475

include/irrMap.h

@@ -132,6 +132,8 @@ class map
 	public:
 
 	typedef RBTree<KeyType,ValueType> Node;
+	// We need the forwad declaration for the friend declaration
+	class ConstIterator;
 
 	//! Normal Iterator
 	class Iterator