Slight refactoring of isolation setting from r10029.
Slight refactoring of isolation setting from r10029.

There was a bug in the way we were reading the DATABASE_OPTIONS setting
and a lot of essentially duplicated code. This is neater.

git-svn-id: 4f9f921b081c523744c7bf24d959a0db39629563@10033 bcc190cf-cafb-0310-a4f2-bffc1f526a37

t11e/django,skevy/django,sam-tsai/django-old,alex/django-old,django-nonrel/django-nonrel,sam-tsai/django-old,sam-tsai/django-old,mitsuhiko/django,t11e/django,mitsuhiko/django,Smarsh/django,jamespacileo/django-france,skevy/django,Smarsh/django,Smarsh/django,Instagram/django,django-nonrel/django-nonrel,mitsuhiko/django,Instagram/django,jamespacileo/django-france,alex/django-old,django-nonrel/django-nonrel,bfirsh/django-old,skevy/django,jamespacileo/django-france,t11e/django,disqus/django-old,bfirsh/django-old,disqus/django-old,Smarsh/django,Instagram/django,alex/django-old,disqus/django-old,sam-tsai/django-old,bfirsh/django-old