Rudimentary DTrace IO provider going in in one week...

Howdy,

I'd really like this code:

http://people.freebsd.org/~gnn/dtio_provider_2.diff

to get some review before I commit it to HEAD.  In particular I'd like
people to try and test it but also I want to know:

*) Is the code organization correct?

The way that DTrace was imported had some issues and I don't fix them here.

*) Are people OK with the module names?

I did what DTrace on Solaris did because that makes using scripts in the DTraceToolkit
an the DTrace book easier.

Best,
George