sunspot/sunspot — pull request #328 by zsiec (2012-12-09 06:40:45+00:00)
Title: Allowing for a user-defined custom seed value to be passed to the RandomSortField

Recently I was working on a paginated collection that had be configured to return a random sort order. I realized that because sunspot always sends Solr a random seed value, I would intermittently receive duplicate results between pages. In order to fix this, I thought it useful to be able to configure the seed value while searching.

The implementation I thought would make the most sense would retain the existing syntax specifications while also allowing a new paramater type to the `order_by` function.

__E.g.__

Existing syntax will continue to work
```ruby
Model.search do
order_by :random, :asc
end
```
or
```ruby
Model.search do
order_by_random
end
```

Proposed alternative
```ruby
Model.search do
order_by :random, :seed => 12345, :direction => :asc
end
```