Fixed a bug with combined server-side sort and paged result controls

Combining server-side sort with paged result controls requires us to use an entryIDSet where the entryIDs are ordered so further paging can restart where it previously stopped.
Since defined EntryIDSets now hold a sorted long array, EntryIDSet cannot be used to store the result of server side sorting.
This change uses a long array to hold the result of server side sorting.

EntryContainer.java:
In search() and searchIndexed(), use a long array instead of an EntryIDSet.

EntryIDSet.java:
Added toLongArray() as a convenience method.