Added oplog_replay to Protocol::Query flags.

[CodeMonkeySteve]

Allow for selective tailing of the oplog, as documented in the Wire Protocol (sort of), and to maintain feature parity with the official Ruby driver.

[coveralls]

Coverage increased (+1.96%) to 95.64% when pulling f59f1ed on apptentive-engineering:oplog_replay into 10abbf3 on mongoid:master.

[coveralls]

Coverage increased (+1.96%) to 95.64% when pulling f59f1ed on apptentive-engineering:oplog_replay into 10abbf3 on mongoid:master.

[coveralls]

Coverage increased (+1.98%) to 95.66% when pulling f59f1ed on apptentive-engineering:oplog_replay into 10abbf3 on mongoid:master.

[coveralls]

Coverage decreased (-0.34%) to 93.34% when pulling f59f1ed on apptentive-engineering:oplog_replay into 10abbf3 on mongoid:master.