Tests: Changes to Travis
Tests: Changes to Travis

* Drop testing development versions of Python for now, esp. as some
  do not even seem to exist anymore.

* Try to get scons installed in the system, as Python3 virtualenvs
  on Travis seem to shadow all Python2 binaries in PATH.

kayhayen/Nuitka,kayhayen/Nuitka,kayhayen/Nuitka,kayhayen/Nuitka