This dramatically improves performance on PyPy. The following benchmark:
python -mtimeit -s "from django.utils.functional import allow_lazy; from django.utils.translation import ugettext_lazy; f = allow_lazy(lambda s: s, str)" "f(ugettext_lazy('abc'))"
goes from 390us per loop to 165us.
Backport of 82e0cd15711c7171aed7af5e481967cc721c9642 from master