Make extending SOCIAL_AUTH_PIPELINE easier

[geweb7]

Now we need to inlude all the default

SOCIAL_AUTH_PIPELINE = (
'social.pipeline.social_auth.social_details',
'social.pipeline.social_auth.social_uid',
'social.pipeline.social_auth.auth_allowed',
'social.pipeline.social_auth.social_user',
'social.pipeline.user.get_username',
'social.pipeline.user.create_user',
'social.pipeline.social_auth.associate_user',
'social.pipeline.social_auth.load_extra_data',
'social.pipeline.user.user_details',
'myproject.models.user_profile_data',
)

into settings to add a single line.

But the default SOCIAL_AUTH_PIPELINE can be changed in the future.
So it would be better to provide some option to add (or remove) just one line.
Something like:
SOCIAL_AUTH_PIPELINE += ('myproject.models.user_profile_data',)

[omab]

@russian-master, now you can do:

from social.pipeline import DEFAULT_AUTH_PIPELINE

SOCIAL_AUTH_PIPELINE = DEFAULT_AUTH_PIPELINE + ('myproject.models.user_profile_data',)