add comments to utility files

Cython/Utility/Builtins.c

+/*
+ * Special implementations of built-in functions and methods.
+ *
+ * Optional optimisations for builtins are in Optimize.c.
+ *
+ * General object operations and protocols are in ObjectHandling.c.
+ */
 
 //////////////////// Globals.proto ////////////////////
 

Cython/Utility/ObjectHandling.c

+/*
+ * General object operations and protocol implementations,
+ * including their specialisations for certain builtins.
+ *
+ * Optional optimisations for builtins are in Optimize.c.
+ *
+ * Required replacements of builtins are in Builtins.c.
+ */
+
 /////////////// RaiseNoneIterError.proto ///////////////
 
 static CYTHON_INLINE void __Pyx_RaiseNoneNotIterableError(void);

Cython/Utility/Optimize.c

+/*
+ * Optional optimisations of built-in functions and methods.
+ *
+ * Required replacements of builtins are in Builtins.c.
+ *
+ * General object operations and protocols are in ObjectHandling.c.
+ */
+
 /////////////// append.proto ///////////////
 
 static CYTHON_INLINE PyObject* __Pyx_PyObject_Append(PyObject* L, PyObject* x); /*proto*/