Today a call to PendingDeletes#numPendingDeletes might return 0
if the deletes are written to disk. This doesn't mean these values are committed
or refreshed in the latest reader. Some places in IW use these numbers to make
decisions if there has been deletes added since last time checked (BufferedUpdateStream)
which can cause wrong (while not fatal) decision ie. to kick of new merges.
Now this API is made protected and not visible outside of PendingDeletes to prevent
any kind of confusion. The APIs now allow to get absolute numbers of getDelCount and numDocs
which have the same name and semantics as their relatives on IndexReader/Writer