AR bug with :include and nested conditions hash

A find like the following produces an sql error because the eager
loading logic does not join to the bank_accounts table.

User.find(:all,:include=>:bank_accounts, :conditions=>{:bank_accounts=>
{:name=>'ICICI'}})

The issue and proposed resolution are documented in the following
ticket.

https://rails.lighthouseapp.com/projects/8994/tickets/2596-include-and-nested-conditions-hash

Please review this patch.

Thanks,

Anthony