Booktype instance doesn't run because use of requires_model_validation

 In a fresh git installation of Booktype 2.1.0 over Debian 8.0 with virtualenv, after fixing django-celery errors importing timeutils, if I try to run Django's server, I have this error:

(booktype) root@dcarrerasrv:/var/www/html/booktype_instance1# ls
booktype2mpdf.php booktype.env booktype_instance1_site conf data database.sqlite lib logs manage.py static themes vendor
(booktype) root@dcarrerasrv:/var/www/html/booktype_instance1# ./manage.py runserver 0.0.0.0:80
Traceback (most recent call last):
File "./manage.py", line 23, in <module>
execute_from_command_line(sys.argv)
File "/var/www/booktype/local/lib/python2.7/site-packages/django/core/management/_init_.py", line 385, in execute_from_command_line
utility.execute()
File "/var/www/booktype/local/lib/python2.7/site-packages/django/core/management/_init_.py", line 377, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/var/www/booktype/local/lib/python2.7/site-packages/django/core/management/_init_.py", line 238, in fetch_command
klass = load_command_class(app_name, subcommand)
File "/var/www/booktype/local/lib/python2.7/site-packages/django/core/management/_init_.py", line 42, in load_command_class
return module.Command()
File "/var/www/booktype/local/lib/python2.7/site-packages/django/core/management/base.py", line 228, in _init_
'"requires_system_checks".' % self._class.name_)
django.core.exceptions.ImproperlyConfigured: Command Command defines both "requires_model_validation" and "requires_system_checks", which is illegal. Use only "requires_system_checks".

Also I have fixed the requires_model_validation issue in django-celery aplying this patch:

https://github.com/celery/django-celery/commit/86f79c441b94ebf42bbefd14746ec8fa56e75237

Pip freeze:

alabaster==0.7.9
amqp==2.1.1
anyjson==0.3.3
Babel==2.3.4
BeautifulSoup==3.2.1
billiard==3.5.0.2
celery==4.0.0
Django==1.7.8
django-appconf==1.0.2
django-braces==1.10.0
django-celery==3.1.17
django-compressor==1.5
django-debug-toolbar==1.3.0
django-devserver==0.8.0
django-discover-runner==1.0
docutils==0.12
-e git://github.com/aerkalov/ebooklib.git@b7005c57602eeea06358ac569a4cf52c630a32ef#egg=EbookLib
factory-boy==2.7.0
fake-factory==0.7.2
funcsigs==1.0.2
imagesize==0.7.1
ipaddress==1.0.17
Jinja2==2.8
kombu==4.0.0
lxml==3.6.4
MarkupSafe==0.23
mock==2.0.0
pbr==1.10.0
pep8==1.7.0
pika==0.10.0
Pillow==2.9.0
psycopg2==2.6.2
Pygments==2.1.3
python-dateutil==2.5.3
Python-OOXML==0.13
pytz==2016.7
redis==2.9.1
requests==2.9.1
selenium==3.0.1
six==1.10.0
snowballstemmer==1.2.1
Sphinx==1.4.8
sqlparse==0.1.19
Unidecode==0.4.19
Unipath==1.1
vine==1.1.3