remove at(index) reference function

remove chrUpr and chrLwr from PIString

libs/main/containers/pimap.h

@@ -206,7 +206,6 @@ public:
 		return pim_content.back();
 	}
 	const T operator [](const Key & key) const {bool f(false); ssize_t i = _find(key, f); if (f) return pim_content[pim_index[i].index]; return T();}
-	T & at(const Key & key) {return (*this)[key];}
 	const T at(const Key & key) const {return (*this)[key];}
 	
 	PIMap<Key, T> & operator <<(const PIMap<Key, T> & other) {