rails/rails — pull request #8060 by senny (2012-10-29 08:06:06+00:00)
Title: descriptive error message when AR adapter was not found. Closes #7313

The error message currently looks like:

```
LoadError: could not load 'active_record/connection_adapters/non-existing_adapter'. Make sure to add the necessary adapter gem to your Gemfile:
sqlite3:	gem 'sqlite3'
postgres:	gem 'pg'
mysql:	gem 'mysql2'
```

This is a fix for #7313