www/py-django-contrib-comments: Use Django 1.6 for RUN_DEPENDS

Default to using Django 1.6 (www/py-django16) because the current version
of www/py-django-mezzanine does not support anything later than 1.6, and
installation currently causes a conflict as installation of both django16
and django18 are attempted:

    py-django-mezzanine -> www/django16, www/py-django-contrib-comments
    py-django-contrib-comments -> www/django (1.8)

This fixes a new (py-django-mezzanine) failure in 2015Q4 reported by
pkg-fallout.

This is the least of all current evils, without having to update Mezzanine
to it's latest versions (*and* have to MFH that update). It has zero impact
on other ports as mezzanine is the only port that currently consumes/depends
on it.

While I'm here, switch back to file-based dependency declaration because
django* matches all django packages, and we can't anchor using $, resulting
in `pkg info "$1" potentially returning multiple matches.

Scripts/do-depends.sh should probably check for multiple results
and error out if there is.

Reviewed by:		antoine
MFH:			2015Q4 (pre-approved: antoine)
Differential Revision:	https://reviews.freebsd.org/D4047

www/py-django-contrib-comments/Makefile

@@ -3,6 +3,7 @@
 
 PORTNAME=	django-contrib-comments
 PORTVERSION=	1.6.1
+PORTREVISION=	1
 CATEGORIES=	www python
 MASTER_SITES=	CHEESESHOP
 PKGNAMEPREFIX=	${PYTHON_PKGNAMEPREFIX}
@@ -13,7 +14,7 @@ COMMENT=	Code formerly known as django.contrib.comments
 LICENSE=	BSD3CLAUSE
 LICENSE_FILE=	${WRKSRC}/LICENSE.txt
 
-RUN_DEPENDS=	${PYTHON_PKGNAMEPREFIX}django*>=1.5:${PORTSDIR}/www/py-django
+RUN_DEPENDS=	${PYTHON_SITELIBDIR}/django/bin/django-admin.py:${PORTSDIR}/www/py-django16
 
 USES=		python
 USE_PYTHON=	autoplist distutils