[Xcb] reason for xcb_parts being 2 elements larger?

[Thomas Hunger]

On Tuesday 04 September 2007, Barton C Massey wrote:
> IIRC positions 0 and 1 are reserved for various kinds of
> header information that also have to go out, to avoid having
> to allocate a new iovec and copy.  Somebody correct me if
> I'm wrong...

You are right, I tracked it down with git. 

I believe this was done to avoid an extra malloc for just 2 iovec 
elements, so it is alloced on the stack by the one calling 
xcb_send_request.

Tom