packaging: Debian testing requires use of tcl/tk 8.6

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
python: fix exception in set_translation_domain

The value from the earlier MultiFileBuilder.set_translation_domain call
was not being passed down to the actual builder object.  Instead, an
exception occurred.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>