ZioBuf: replace invalid name 'el' with 'tmp'

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
ZioBuf: verify that 'flush' exists before use it

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
ZioChan: simplify code

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
PyZio: fix comments
PyZio: apply PyDev suggestions
ZioInterface: fix comment typo
ZioCset: check that an attribute exist before use it
ZioError: add internal errors

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
ZioChan: raise ZioInvalidControl if user try to write invalid control

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
ZioCset: raise ZioMissingAttribute on missing attributes
ZioCtrl: rename zCtrlAttr -> ZioCtrlAttr
PyZio: apply new-style class
PyZio: fix PyDev warnings