#13 Additional PROM Data / Cleaned up interfaces

[Thomas Preußer]

The attached patch contains multiple contributions:
- Feature:
- allow additional data to be appended to bitfile for
programming platform flashes (PROMs)
- usage() documentation extended
- Code Structure:
- stronger encapsulation in iobase and subclasses
- error flagging in io device replaced by exception
throwing
- auto_ptr instead of two redundant stack instances
of all supported io devices
- fallback to environment variable or default moved
into affected entity - triggered by a NULL argument

[Thomas Preußer]

Patch against SVN 2008-03-05

[Uwe Bonnes]

Included and hopefully working in maintanance release 1436