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* 250: Install '-nspkg.pth' files for packages installed
with 'setup.py develop'. These .pth files allow
namespace packages installed by pip or develop to
co-mingle. This change required the removal of the
change for 805 and pip 1924, introduced in 28.3.0 and implicated
in 870, but means that namespace packages not in a
site packages directory will no longer work on Python
earlier than 3.5, whereas before they would work on
Python not earlier than 3.3.