--force was replaced in favor of --clear and --upgrade which
correspond to the respective pyvenv options. The pyvenv help is
not explicit on the behavior if --clear is not given but the path
exists. https://docs.python.org/3/library/venv.html states pyvenv
would fail in that case, but it does not with Python 3.4.2, which
I don't consider a problem however.
Added a newline here and there for better readability.
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