mperham/dalli — pull request #365 by pitr (2013-05-16 15:18:20+00:00)
Title: ADD - or `write(unless_exist:true)` -  is broken due to LocalStore

adding a breaking spec. The ideal flow is:

```ruby
@dalli.write('key', 123, unless_exist: true) # => true
@dalli.write('key', 321, unless_exist: true) # => false
@dalli.read('key') # => 123
```