[ale] GPU acceleration

[David Hilvert]

There's been earlier discussion of acceleration via specialized hardware, among
which (if they can be called specialized) GPUs are perhaps the most generally
available, and also easily able to do such useful things as projective
transformations.  As Gregory Maxwell had earlier noted, having some sort of
acceleration would be especially useful for video processing, where GPUs could
likely accelerate alignment tasks, and perhaps also rendering.  

Are any reasonably common libraries available that would be useful for this
sort of thing?  (Currently, I am vaguely imagining using one of the X-related
libraries.)  Also, if someone wanted to write demonstration code using such a
library for something like alignment (rendering would be OK, too), this would
probably be useful.  (If not, I will probably get to this sometime after the
next release.)