Fixed #22372 -- Improved description of WizardView.get_context_data().

Thanks simon29 for the report.
Fixed typo in 1.8 release notes.
Cleaned up string detection for a deprecation warning by using six.string_types.
Fixed #22363 -- Correctly serialize `django.utils.datetime_safe` objects.

Thanks to linovia for the report.
Refactored and commented strip_tags utility
Fixed #22380 -- Missing SECRET_KEY variable in sample settings file for testing
Merge pull request #2514 from vlal/ticket_22380

Fixed #22380 -- Missing SECRET_KEY variable in sample settings file for ...
Fixed case in form widgets docs
Fixed #21649 -- Added optional invalidation of sessions when user password changes.

Thanks Paul McMillan, Aymeric Augustin, and Erik Romijn for reviews.
Fixed #22236 -- Removed inappropriate usage of signals

Thanks Aymeric Augustin for the report and Tim Graham for the review.
Fixed #22216 -- Added Form.non_field_errors to form API doc.
Fixed #21977 -- Deprecated SimpleTestCase.urls
Removed casting to bool just before negation.
Fixed #21084 -- Used proxy model's content type for admin log entries.
Fixed #21084 -- Used proxy model's content type for admin log entries.

(the previous commit included only the test)
Added missing request parameter to get_current_site().
Fixed #22405 -- Fixed string error in models/queries docs.
Fixed #9535 -- Added a reference guide for file upload classes.
Fixed some spelling issues in docs.
Added Python 3.4 to list of supported version in docs/intro/install.txt