intridea/grape — pull request #632 by fixme (2014-04-18 19:50:49+00:00)
Title: endpoint#present makes needless sql query

Hey, here is some fix to prevent needless sql query in endpoint#present method, because of #first method usage on activerecord relations.
Example:
```ruby
author = Author.find params[:id]
present author.books
```
it makes an additional sql query on `books` relation because of #first method usage in entity's auto-detection block.