Fixed #13418 -- Added notes on uniqueness requirements for natural keys. Thanks to hunajakippo for the suggestion, and Ramiro Morales for the draft text.
Fixed #13418 -- Added notes on uniqueness requirements for natural keys. Thanks to hunajakippo for the suggestion, and Ramiro Morales for the draft text.

git-svn-id: 554f83ef17aa7291f84efa897c1acfc5d0035373@13146 bcc190cf-cafb-0310-a4f2-bffc1f526a37

svn2github/django,svn2github/django,svn2github/django