bigarray compiler speedups could help cstruct too

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

Yaron just pointed me to some cool patches that Pierre and Thomas are working 
on at OCamlPro to speed up Bigarray accesses directly.

http://caml.inria.fr/mantis/view.php?id=5771

These will greatly speed up cstruct (and hence our I/O parsing stack), since 
right now the cstruct generated code goes through C function calls for each 
access, whereas these 'builtins' are direct compiler hints.

Pierre, Thomas, can this be extended to work with different endians as well? 
For network traffic, we almost always have to do an endian swap...

-anil