Merging ATA passthru

[Jeff Garzik <jgarzik@pobox.com>]

Folks,

Taking Mark Lord's (and others) criticism to heart, I'm going to merge 
the ATA passthru work upstream, once 2.6.14 is released.

Since there are still some reported problems that I haven't had time to 
track down, I'm going to -- like ATAPI -- introduce a module option that 
enables passthru.  It will default to off.

Other features that follow a similar pattern -- 98% there but needs a 
few final tweaks -- will be treated in the same way.

This gets lesser-used features upstream where they can get the most 
testing, while defaulting them to off ensures that we won't perturb the 
known-working code.

This also will help me, in that I won't have to maintain a bunch of 
parallel codebases.

	Jeff