[bin/morse] Check precisely that morse python version matches blender one

This commit also remove the output of PYTHONPATH, because, in the case
of a bad interpreter version, it triggers an exception, which is not
easy to understand by user.

While here, fix some too much long string, and simplify import dance, as
it can be only configured with python3.2+
[testing] Add some regression test for multiple humans (#308)