IOCTL exceptions in kbus.py are not user-friendly

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Various KBUS operations use IOCTLs, and in Python these result in IOError 
exceptions, with a "magic number" inside to indicate the particular 
problem (and a standard Unix interpretation of said number, as a string).

At the C level, this is perfectly sane and traditional, but to a Python 
programmer it is not. In the Python context, it would be more helpful to 
turn these IOError exceptions into something closer to the *actual* 
explanation (as descrined in the KBUS documentation).

Rationale: well, it confuses me, and I wrote the code.

Original issue reported on code.google.com by t...@tibsnjoan.co.uk on 21 Sep 2009 at 2:31