Support other Rails environments besides development, test and production

Rails supports the ability to easily add additional runtime environments beyond development, test and production. I may see in 'adhearsion-0.8.3/lib/adhearsion/initializer/configuration.rb' (line 227) we are restricting to only the standard ones.

There are times we may want to add an additional environment, such as 'adhearsion_jruby', that would allow Adhearsion to share the models while using JDBC/JRuby, while Rails runs on the MRI/EE under Passenger.

Would be best to set the constant SUPPORTED_RAILS_ENVIRONMENTS in startup.rb.