This goes on top of the other enumeration patch I just sent,
to handle some dubious and/or broken hub configurations better.


Make khubd handle some cases better:

 - Track power budget for bus-powered hubs.  This version only warns
   when the budgets are exceeded.  Eventually, the budgets should help
   prevent such errors.

 - Rejects illegal USB setup:  two consecutive bus powered hubs
   would exceed the voltage drop budget, causing much flakiness.

 - For hosts with high speed hubs, warn when devices are hooked up
   to full speed hubs if they'd be faster on a high speed one.

 - For hubs that don't do power switching, don't try to use it

 - For hubs that aren't self-powered, don't report local power status