Prefer setImmediate over process.nextTick

Hello @sboora, @nicks, @dpup, @x-ma, 

Please review the following commits I made in branch 'nathan-setImmediate'.

b674c3cec3688b3552a56c1c348569bf85b79934 (2014-09-16 15:37:01 -0700)
Prefer setImmediate over process.nextTick

R=@sboora
R=@nicks
R=@dpup
R=@x-ma