This method will be used to find out when a permanode or claim
was (un)deleted for the last time.
This change also introduces the keyDeletes index entry which
allows to find the permanodes/claims that a delete claim deletes.
Finally, since some index keys have changed, this CL introduces
a check for an index schema version, to force users to reindex
when needed.
http://camlistore.org/issue/191
Change-Id: I6f8e5d3030a6ddc8b21ff5dc5db311f2ea16f613
mpl