Add allSettled()

Hello @nicks, @dpup, 

Please review the following commits I made in branch 'xiao-add-allSettled'.

90c71514858197fca51ca7bcb831b5087c6ff7e6 (2014-01-10 18:55:26 -0800)
Add allSettled()

R=@nicks
R=@dpup
VISIBLE_CHANGES=Add allSettled()