[backends] Added better error handling when parsing the <backend>_EXTRA_DATA setting
Merge pull request #766 from shootitlive/master

[backends] Added better error handling when parsing the <backend>_EXTRA_DATA setting
Fixes losing of "access" or "refresh" tokens issue
Merge pull request #767 from marselester/master

It fixes losing of "access" or "refresh" tokens issue
Merge branch 'master' into psa2

Conflicts:
	social_auth/backends/__init__.py
	social_auth/db/base.py
	social_auth/exceptions.py