Bug#972349: b-d's on python3-all-dev, but only builds for the default python3

[Matthias Klose]

Package: src:getfem++
Version: 5.3+dfsg1-3

getfem++ b-d's on python3-all-dev, but only builds for the default python3
version.

Either b-d on python3-dev, or build for all supported python3 versions.