ActionMailer::Base.perform_deliveries to accept a proc

Here's a patch so that ActionMailer::Base.perform_deliveries will accept a proc -

currently it expects a boolean -

I wanted to easily perform deliveries conditionally in my staging environment - only sending mails where recipient is in certain domain. I can achieve this with a quick but brittle monkey patch.

ActionMailer::Base.perform_deliveries = lambda {|mail| mail.header['to'].to_s =~ /@example.com$/}