Bug#724314: steam: Lower version than was previously in the Debian archive

[Felix Geyer]

Source: steam
Version: 1.0.0.39-2

The current steam package has a lower version than the old steam package
that was previously in the Debian archive (1.0.0.39-2 << 2.2.31-6).
I suggest adding an epoch to the version number.

Looks like the package has been accepted in the first place because of
bug #620356 in dak.