Tell Qt4 that we really meant Utf8 when we said Utf8

How strange. Telling Qt4 to assume that all C strings are Utf8 apparently
isn't enough to convince tr() that the C strings we pass to it are Utf8.
You need to set that codec separately.

Fixes #503

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>