Display original exception in test mode

This is very useful when running specs with `config.consider_all_requests_local = false` `config.action_dispatch.show_exceptions = true`: this displays the "real" error message that is also displayed to the user in production mode. To make debugging failing specs easier, displaying the original exception is very useful.
Add light red color background to original exception
Revert some accidents
Display errors also in development. Downcase color code.
Merge pull request #13 from jmuheim/master

Display original exception in test mode