less esoteric parameter passing to processProject()

just pass around fully qualified file names instead of QFileInfos.
a side effect of this is that error messages use full paths as well -
this can be considered good or not.

Change-Id: I55a7545064d32ac717ce9c57205ef59b76afc3f0
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>