Do not use instance variable.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@7897 e93f8b46-1217-0410-a6f0-8f06a7374b81
Do not use .merge_conditions.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@7898 e93f8b46-1217-0410-a6f0-8f06a7374b81
Prevent clash with Rails 3 Query module.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@7899 e93f8b46-1217-0410-a6f0-8f06a7374b81