create _version.py in build step, not install step
create _version.py in build step, not install step

This fixes dependencies not being installed when running
'setup.py install'. The cause was a workaround in the
setuptools 'install' class, that uses call stack inspection
to modify behavior for the sake of backwards compatibility.

ginolhac/mapDamage,ginolhac/mapDamage,ginolhac/mapDamage