This is somewhat related to Bug#818201, in that it
involves that fact that the --build-base option only
appears to be operational under the build command.

Hence it is not possible to do:

python setup.py install -b <somedir>

The --help for install does not say that one can, so
the situation is not as inconsistent as in the previous
bug report. Nevertheless, it is problematic that once
one does:

python setup.py build -b <somedir>

as far as I can tell there is _no way_ to just install
the result.

One needs to always do:

python setup.py build -b <somedir> install

This seems somewhat unwieldy; perhaps -b should be
more universally available to all distutil commands?