Restore pad to new location at a given revision

This script gives an admin with shell access the ability to restore a
pad at a given revision by essentially rebuilding it at a new location
with data associated with the original pad.  The upsides to creating a
new pad vs. changing the original are: 1) avoiding service disruptions
(no deletes, no moving targets - builds from previous revision); and 2)
preservation of data (no deletes, no overwriting of the source pad).
The most obvious downside is the pad has a new ID which could require
folks to update their links, bookmarks, etc. to point at the new
location.