Fixed some awkward wordings from docs/model-api.txt from [5519] and added 'new in Django development version' notes
Fixed some awkward wordings from docs/model-api.txt from [5519] and added 'new in Django development version' notes

git-svn-id: 554f83ef17aa7291f84efa897c1acfc5d0035373@5560 bcc190cf-cafb-0310-a4f2-bffc1f526a37

svn2github/django,svn2github/django,svn2github/django