Revert hacks now that we use Qt5 on Mac

Commits a24eb8ac120bf and 0b0860d24a81b introduced a nasty hack that was
needed back then to make tank and weight selection work on the Mac. But it
caused other unpleasant issues (as mentioned in the commit messages).

I re-tested this with the current Qt5.3 based builds on Mac and this hack
is no longer needed.

Fixes #638

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