O_DIRECT

[Dan Stromberg]

It'd be pretty cool if rsync supported use of O_DIRECT on platforms that
support it, with or without my odirect package:

http://dcs.nac.uci.edu/~strombrg/odirect/

I say this because rsync is sometimes used to move a mountain of data,
just once.  So there's little point in rsync toasting one's buffer cache.

I gather there's something like O_DIRECT on windows too, but it's mostly
Linux and FreeBSD I'm interested in.