Also removed debugger from development dependency since a different package is required for each version of Ruby (1.8, 1.9 and 2.0). It can still be added ad-hoc during development. Just not making it a permanent part of the development requirements.
Not sure how the one test was previously passing. Also we should have been using get all along but it is now required in Rails 4.
This also works in Rails 3.2. It was probably previously wrong and just happened to work.
The isolation only caused problems because the layout couldn't access application routes. A isolated engine really needs it's own layout. But that would defeat the whole purpose of the gem. The namespacing of the models and controllers provides enough isolation.
Error message and backtrace are sent to the log. A simple message without a layout is sent to the website.
Checking files on every exception is not that expensive and it stops us from having to bounce the server whenever we add/remove a template. I'm not completely sure why the bouncing was necessary. Seems that the exception would be fresh each time. But perhaps I am missing something so just removing caching for now.