Ticket #3271: New methods for Data.Sequence

I'm finished with Ticket #3271: New methods for Data.Sequence. I'd like someone to at least briefly review it before committing it, but I'm pretty sure I've done everything right. I think there are some separate, Cabal-based issues with containers (specifically, I need to amend containers.cabal to depend on base>=4.0.0.0, but that should be a separate bug), but I'm confident in everything there currently, and QuickCheck confirms that all of the added methods behave analogously to their Data.List counterparts. Louis Wasserman wasserman.louis@gmail.com