default action_mailer.perform_deliveries to false

for development, don’t send emails by default.  Undid the change made
in 07a599d12be9f8928493d5d65203e91efa4aad27 to toggle delivery using an
environment variable.  Environment variables are just strings, so both
“true” and “false” were evaluating to true.  I thought this was working
at home, but now realized that was just because I wasn’t on the  JMU
network so I couldn’t hit the SMTP server to deliver mail.

So, for the simplest solution, just don’t deliver mail in development.
If you need to deliver mail, just toggle the setting in development.rb,
but don’t commit it ;)