Fixed #19954 -- Fixed MySQL _last_executed decoding

Queries can contain binary data undecodable with utf-8. In this
case, using the 'replace' errors mode when decoding seems like
an acceptable representation of the query.
Thanks Marcel Ryser for the report.
Added 1.5.1 release notes.
Updated the release document after actually doing a release (!).
Minor updates to 'How is Django Formed.'
Fixed #20146 -- Updated removed_tags example
Merge pull request #956 from maikhoepfel/master

Removed ambiguity regarding LANGUAGES setting
Improved FormView docs in class-based views index.

Thanks Stefan Berder.
Fix #20158: invalid code in queryset_pickle test models.
Merge pull request #975 from bmispelon/ticket-20158

Fix #20158: invalid code in queryset_pickle test models.
Fixed #14540 -- Added Porto-Rico specific formats

Thanks rosarior for the report and the file proposal.
Fixed #20159 -- Mispelled attribute in multi-db documentation example.

Thanks to sane4ka.sh at gmail for the report!
Fixed #20160 -- Erronous reference to `module_name` in admin doc.

Ref #19689.
Fixed #20150 -- Fixed an error in manager doc example
Fixed setup.py overlaid-install warning.

Before this change, if you had a global Django installation in /usr/local/, you
might get a spurious warning when installing Django within a virtualenv.

Thanks epicserve for the report and debugging help.
Merge pull request #977 from nims11/ticket_20150

Fixed #20150 -- Fixed an error in manager doc example
Fixed #15379 - Added "how to cite Django" to FAQ.

Thanks Russ and Susan Tan.
Fixed #19582 - Added a static files tutorial.

Thanks James Pic.
Fixed #19897 - Updated static files howto.

Thanks Jan Murre, Reinout van Rees and Wim Feijen,
plus Remco Wendt for reviewing.
Fixed #19998 -- Fixed --ignorenonexistent support for XML based fixtures.
Fixed #20130 -- Regression in {% cache %} template tag.