Add a destroy callback for the list plugin

- When an item is deleted from a list, the positions
  of the following items need to be decremented to fill in the gap.
Minor cleanups for list plugin destory handling

Update existing rows after removal of current row, works better
when there is a unique index.  Don't use raw SQL in the update
query.  Add integration tests.
Raise error within manual admin disconnection

Raise error Sequel::DatabaseDisconnectError when receiving the message
"terminating connection due to administrator command". This may happen
with a manual restart or any other manual connection reset.
Merge commit '5c03fca'
Update CHANGELOG
Update sql.rdoc for consistency
Merge branch 'patch-1' of https://github.com/arturoherrero/sequel