Refs #752 Paged aggregate queries will re-use the partition_slice object, thus when setting a specific ck range for "last pk", we will hit an exception case. Allow removing entries (actually only the one), and overwriting (using schema equality for keys), so we maintain the interface while allowing the pager code to re-set the ck range for previous page pass. [tgrabiec: commit log cleanup, fixed issue ref] Message-Id: <1452616259-23751-1-git-send-email-calle@scylladb.com>