www/py-django-dpaste: Update to 2.9

• Update to 2.9. This fixes run-time and tests with www/django (1.8)
• Use Django 1.8 for RUN_DEPENDS
• Switch to USE_GITHUB (no new sources at PyPI)

Default to using Django 1.8 (www/py-django) because the current
version of www/py-django-mptt (a dependency) defaults to installing 1.8.

Installation currently causes a conflict as installation of both django16
and django18 are attempted:

py-django-dpaste -> www/django16, www/py-django-mptt
py-django-mptt -> www/django (1.8)

This fixes a failure in the quarterly ports branch reported by pkg-fallout.

Reviewed by: antoine
MFH: 2015Q4 (pre-approved: antoine)
Differential Revision: https://reviews.freebsd.org/D4048