Tweak COMMENT.
## Rails 3.1.4 (unreleased) ##
* Fix a custom primary key regression *GH 3987*
*Jon Leighton*
* Perf fix (second try): don't load records for `has many :dependent =>
:delete_all` *GH 3672*
*Jon Leighton*
* Fix accessing `proxy_association` method from an association extension
where the calls are chained. *GH #3890*
(E.g. `post.comments.where(bla).my_proxy_method`)
*Jon Leighton*
* Perf fix: MySQL primary key lookup was still slow for very large
tables. *GH 3678*
*Kenny J*
* Perf fix: If a table has no primary key, don't repeatedly ask the database
for it.
*Julius de Bruijn*
fe21f83891