copy bufio.scan to change MaxScanTokenSize
Adding oplog with large entry so that we can test against that
Merge pull request #9 from Clever/allow-large-scans

copy bufio.scan to change MaxScanTokenSize
Code review comments
Merge pull request #11 from Clever/review-feedback

Review feedback
Support fixed rate oplog replaying (ops per second)

This change adds an interface for controlling the rate at which we apply
op logs. Theoretically this interface could control the rate at which
more generic things are done. Though it's similar to the leakybucket
abstraction we already have, the relative rate ideas we have didn't
cleanly map onto the leakybucket so I thought this new interface was
useful.

This change also adds to implementations of the interface. The fixed and
relative rate controllers we want for oplogs. It also adds a new command
line parameter to control which rate controller we use in the replay. It
defaults to the fixed rate.