Changed API to disable ATOMIC_REQUESTS per view.

A decorator is easier to apply to CBVs. Backwards compatibility isn't an
issue here, except for people running on a recent clone of master.

Fixed a few minor problems in the transactions docs while I was there.
Merge pull request #1181 from aaugustin/better-api-to-disable-atomic-requests

Changed API to disable ATOMIC_REQUESTS per view.