This fixes a situation when there are multiple backups--if the master
dies, both backups promote themselves simultaneously. If we add in
advskew, this allows the backup with the lower advskew to promote itself
while the backup with the higher advskew is still waiting.

By Corey Hickey.
Merge branch 'master' of https://github.com/jedisct1/UCarp

* 'master' of https://github.com/jedisct1/UCarp:
  This fixes a situation when there are multiple backups--if the master dies, both backups promote themselves simultaneously. If we add in advskew, this allows the backup with the lower advskew to promote itself while the backup with the higher advskew is still waiting.