rails/rails — pull request #6101 by MSNexploder (2012-05-01 18:50:57+00:00)
Title: Additional index support

Added add_index override in postgresql_adapter and mysql_adapters to allow custom index type support.

```ruby
add_index(:wikis, :body, :method => 'gin')
```

It's basically an updated version of this [older pull request](https://github.com/rails/rails/pull/3706)