[Converge] repl: Private Buffer object in lib/* files

[jasnell]

See: nodejs/node-v0.x-archive@523929c
/cc @trevnorris

The original commit log says, "Fixes usage of global object 'Buffer' in lib/* files by ensuring that each file does an explicit require('buffer').Buffer. Previously, when running a repl, due to usage of global 'Buffer', any redefinition of Buffer would cause a crash eg var Buffer = {}."

[Fishrock123]

This should be ported to io.js.

[Fishrock123]

The plan is to add linting alongside doing an updated version of this. progress here: nodejs/node#1794

[silverwind]

Landed a ported version in nodejs/node@b5b8ff1, notable difference is that the workaround for the race condition wasn't necessary any more.