Fixed #7534 -- Added a note about TEST_DATABASE_CHARSET in the contribution...

Fixed #7534 -- Added a note about TEST_DATABASE_CHARSET in the contribution documentation. Thanks to Peter Melvyn for the suggestion and initial draft. 

git-svn-id: http://code.djangoproject.com/svn/django/trunk@7916 bcc190cf-cafb-0310-a4f2-bffc1f526a37