The compatibility layer for management commands tries to convert

new-style argument definitions to optparse on Django 1.6. However, one

major difference between the two is that argparse supports defining

positional arguments whereas optparse does not allow explicitly

defining these, instead leaving this up to the consuming command.
This change simply filters out the positional argument definitions when

using optparse, avoiding a crash. It still leaves the handling up to

the command, however, passing all positional arguments from the command

line.

Tested management commands defining positional arguments on both

Django 1.6 and 1.11.