rails/rails — pull request #3525 by kennyj (2011-11-05 04:13:30+00:00)
Title: Fixed an issue id false option is ignored on mysql/mysql2 (fix #3440)

In mysql, to look for a primary key, we should use the information_schema than the describe command.
Because when there is no primary key, the describe command reports the not null unique key as primary key.