use file system encoding instead of assumed 'ascii'

Task-number: PYSIDE-211
Change-Id: I4233d093cf2abe1eeb006fd836c10d1ddcbc9858
Reviewed-by: Roman Lacko <backup.rlacko@gmail.com>
Reviewed-by: Christian Tismer <tismer@stackless.com>
Reviewed-by: John Ehresman <jpe@wingware.com>