add fopencookie

See https://issues.dlang.org/show_bug.cgi?id=13755
If I do remove the "extern(C) nothrow {" I get

stdio.d:53: error: cannot implicitly convert expression (&specialRead) of type int delegate(void* cookie, char* buf, uint size) nothrow to extern (C) int function(void* cookie, char* buf, uint size) nothrow

(with gdc 4.9.1)