Copy database sessions.
Retry if the session drops.
Move the session copy into NewDBInfo.
Fix a typo.
Use errors.Cause.
Add a TODO comment about the type conversion.
Retry multiple times if we detect dropped connections.
Add replicaset.IsReady and testing helpers.
Ensure that the replicaset is ready.
Do not worry about reconnecting since we wait for HA to come up.
Do not do the HA check during testing.
Drop the NewServerReplSet testing helper.
haEnabled -> isReady.
Drop WaitUntilReady.
Add tests for IsReady.
Fix a test.
Merge pull request #1259 from ericsnowcurrently/backups-db-eof

Improve handling of EOF during backup-related DB operations.

This is motivated by the following CI test failure: http://juju-ci.vapour.ws:8080/job/functional-ha-backup-restore/1165/console

(Review request: http://reviews.vapour.ws/r/573/)