SERVER-7800 Fix "db.printSlaveReplicationInfo()" command in mongo shell, for replica sets.

It is wrong to compare current slave optime with time at this moment,
because some databases don't changes during some period of time.

Value which we must use to compare with current slave optime is -
master optime.

Signed-off-by: Azat Khuzhin <a3at.mail@gmail.com>
Signed-off-by: matt dannenberg <matt.dannenberg@10gen.com>
SERVER-7800 Fix "db.printSlaveReplicationInfo()" command in mongo shell, for replica sets. cont

changed message to a less confusing
also more pretty (no more tabs + one space)