Fixed #16865 -- Made get_or_create use read database for initial get query.

Thanks Rick van Hattem for the report and trbs for the patch.
Revert "Fixed #16865 -- Made get_or_create use read database for initial get query."

Thanks to Jeremy Dunck for pointing out the problem with this change. If in a
single transaction, the master deletes a record and then get_or_creates a
similar record, under the new behavior the get_or_create would find the record
in the slave db and fail to re-create it, leaving the record nonexistent, which
violates the contract of get_or_create that the record should always exist
afterwards. We need to do everything against the master here in order to ensure
correctness.

This reverts commit 901af865505310a70dd02ea5b3becbf45819b652.
Fixed #13586 - Added an example of how to connect a m2m_changed signal handler.
Fixed #14829 - Added references to CBVs in the URLConf docs; thanks Andrew Willey for the suggestion.
Fixed #15325 - Added a link to RelatedManager in the ManytoManyField docs; thanks jammon for the suggestion.
Added a note about GEOS support for 3D/4D WKT notation

See also http://trac.osgeo.org/geos/ticket/347
Fixed #17687 -- Made LayerMapping router-aware

Thanks nosamanuel@gmail.com for the report and the initial patch.
Fixed #16577 -- Added a map_creation block in openlayers.js template
Imported getLogger directly from logging module

This was a remainder of some 2.4 compatibility code.
Add documentation for get_caches function
Removed an excess colon. Thanks to jMyles for the patch.
Fixed #18934 - Removed versionadded/changed annotations for Django 1.3
Merge pull request #386 from clelland/ticket_15269

Fixed #15269 - Added documentation for get_caches function
Fixed #10853 -- Skipped some sessions tests with dummy cache backend
Fixed #19008 typo in signals docs
Fixed #16835 -- add groups to auth.user admin list_filter
Made geo3d tests independent from each other
Fixed #16218 -- date_list order in generic CBVs.

Thanks nnrcschmdt for the report and bpeschier for the initial
version of the patch.
Fixed #18951 -- Formatting of microseconds.

Thanks olofom at gmail com for the report.
Fixed #18057 - Documented that caches are not cleared after each test; thanks guettli for the suggestion.