Fix a bug in the schema backend that could cause problems when deleting one
instance of an element and adding a different instance of the same element in
the same modification that also depends on a third schema element which was
added between the two.  For example, if you tried to have a single modify
operation that deleted an existing object class, added a new attribute type,
and added a new object class that depended on the new attribute type, the
operation would fail because when processing the removal of the object class
the server would attempt to determine whether it was going to be re-added later
in the operation and therefore attempted to decode any object class additions
later in the operation.  An error occurred when trying to decode the new object
class because it depended on an attribute type that was not yet defined and the
decode operation wasn't told to ignore unknown schema elements.

OpenDS Issue Number:  1318