Fix NumberFormatException in PersistentBinaryDeque.

Don't assume that the files will have the same nonce, break the filenames apart
before checking on the components of the filename.
ENG-4432: Fix extension check in PersistentBinaryDeque.
ENG-4432: Fix PersistentBinaryDeque name parsing to allow '.' in nonce.
ENG-4432: Improve fix readability per Izzy's review comment.
Merge pull request #404 from VoltDB/ENG-4432

ENG-4432: Fix NumberFormatException in PersistentBinaryDeque. r=izzy