3700: Getting a list of all RBs that a user participated in (commented on, ship it, etc) via the API

evan.bo*******@gmai***** (Google Code) (Is this you? Claim this profile.) 
Provide an API endpoint for fetching all of the RBs that a user participated in.

For example, if a user is a member of a large group that gets lots of RBs assigned to them I want to get a list of those specific RBs where the user actually commented or provided a review/ship it without seeing the RBs they didn't participate in.

For more context see the following discussion on the RB group: https://groups.google.com/forum/#!topic/reviewboard/fl0djzlcsDk