Refactor replay

Refactor the replay package.  This change breaks the replay into well separated pipeline stages, namely:

[parse BSON] ---op---> [controlRate] ---op---> [batchOps] ---[]op---> [applyOps]

Each stage controls the lifetime of their own output channels, closing them when appropriate.  Each stage also properly exits early in the case of failure.  The design of the new package is influenced heavily by [this blog post on pipelines](http://blog.golang.org/pipelines)
This update also makes oplog-replay compatible with go 1.3+.
Should be no need.  Both of those break when their input channels are closed.  parseBSON is the only stage that doesn't use this input channel pattern.