Multiple py-backports packages include a site-packages/backports/init.py file, thus causing a failure when trying to activate multiple py-backports packages.

$ ./bin/spack activate py-backports-functools-lru-cache
==> Error: Extension blocked by file: /nfs/tmp2/lee218/delete/spack-basemap/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/python-2.7.14-7rci3jkmuht2uiwp433afigveuf4ocnu/lib/python2.7/site-packages/backports/init.py

$ ls -l opt/spack/linux-rhel7-x86_64/gcc-4.9.3/py-backports*/lib/python2.7/site-packages/backports/init.py
-rw------- 1 lee218 lee218 65 May 12 2017 opt/spack/linux-rhel7-x86_64/gcc-4.9.3/py-backports-functools-lru-cache-1.4-znbn6jwuu6xwpbdvk3mclmcntkcjwuhi/lib/python2.7/site-packages/backports/init.py
-rw------- 1 lee218 lee218 75 Aug 19 2014 opt/spack/linux-rhel7-x86_64/gcc-4.9.3/py-backports-shutil-get-terminal-size-1.0.0-k2m5kjyz4j3cgpntij77xkiwsnqyc627/lib/python2.7/site-packages/backports/init.py
-rw------- 1 lee218 lee218 155 Dec 19 2015 opt/spack/linux-rhel7-x86_64/gcc-4.9.3/py-backports-ssl-match-hostname-3.5.0.1-jsr5wgmh2cfiscwcdptfnov44zna7emk/lib/python2.7/site-packages/backports/init.py

Any thoughts on how to best manage this? Currently all of the init.py files effectively do the same thing:

$ cat opt/spack/linux-rhel7-x86_64/gcc-4.9.3/py-backports*/lib/python2.7/site-packages/backports/init.py__path__ = import('pkgutil').extend_path(path, name)
from pkgutil import extend_path
path = extend_path(path, name)

This is a Python "namespace package" http://www.python.org/dev/peps/pep-0382/

from pkgutil import extend_path
path = extend_path(path, name)