`depend_on` message format is `"No such file to load -- %s.rb"`.
But `require_dependency` message is missing `.rb` suffix.
```
% git grep -n 'No such file to load'
actionview/test/actionpack/abstract/helper_test.rb:112: assert_equal "No such file to load -- very_invalid_file_name.rb", e.message
activesupport/lib/active_support/dependencies.rb:245: def require_dependency(file_name, message = "No such file to load -- %s.rb")
activesupport/lib/active_support/dependencies.rb:333: def depend_on(file_name, message = "No such file to load -- %s.rb")
```
Change most tests to make use of assert_raise returning the raised
exception rather than relying on a combination of flunk + rescue to
check for exception types/messages.
