Default Collapser scope to REQUEST if using Setter

[benjchristensen]

The default is set to REQUEST via the constructor, but it someone uses the Setter fluent interface it doesn't get defaulted.

[benjchristensen]

This isn't causing anything to fail because there is a fallback in queue() to use REQUEST if scope is null, but that safety-net shouldn't be relied upon here.

[benjchristensen]

Committed in 38d85c5