Added test runner option to skip Selenium tests (#19854).
Merge pull request #781 from zsiciarz/ticket_19854

Fixed #19854 -- Added test runner option to skip Selenium tests
Fixed #15877 -- Improved exception when ModelForm has no model class

Thanks theaspect at gmail.com for the report and volrath for the
patch.
Fixed errors introduced in 21f333bcefccc151d6439246f8203d609ab6ca79. Refs #17751
Fixed errors introduced in 664855b74e1f417384dc7aef35a3df5f86db52d6
Changed %r to %s in get_language_info error message.
Merge pull request #791 from khalas/ticket_19811

Changed %r to %s in get_language_info error message
One last final fix for 0ad76843. Tested on py3 and py2
Fixed #19698 -- Cleared sites cache with signals

Thanks ddavies at nomensa.com for the report and the patch and
serdaroncode for reviewing the patch.
Added a draft document explaining how to release Django.

Thanks to James for the first draft; I made a few changes (svn->git) and
some supporting links, but mostly I added FIXME's.
Merged from origin/master