Updating Rakefile to include app tasks

Given that I am working on an engine there are tasks that can be
run within the context of the internal rails application.
Adding config warnings for feature specs

I want to make sure that people see that some part of the
configuration should be set.
Adding tmp/ to list of ignored files
Adding ./script/fast_specs

Cribbed from https://github.com/jimweirich/wyriki/blob/master/script/fast_specs