SERVER-15767 Refuse to start up with invalid locally stored rs config
SERVER-15562 Estimate density before near search
SERVER-15771 Do not step down a remote primary unless you plan to replace it yourself.

Also, when stepping down for a higher priority node, set _electionSleepUntil,
not _stepDownUntil.  This way, lower priority nodes will still consider you
electable, and defer to you.
Revert "SERVER-15767 Refuse to start up with invalid locally stored rs config"

This reverts commit 33d59e5d8cded2e0eab2b9e370727eac5e4d020c.