fsyncLock+auth clarification

On the fsyncLock doc page, we should warn users that fsyncLock may block reads, and hence it may block authentication attempts. So in systems with authentication enabled we recommend to keep the shell you used for fsyncLock() open. This way you will be able to reuse it for Unlock() later.

Usually, users use fsyncLock/Unlock as part of their backup scripts. One way to have a single connection throughout the script is to use a scripting language that has a mongo driver (e.g. not bash but perl or python).