hdf5

Checkin of additions to cache image parallel test code and
associated bug fixes.

Also, modifications to H5PB_dest() to flush the page buffer before
destroying the page buffer.  This is necessary, as when persistant
free space managers are enabled, the page buffer will typically contain
dirty FSM data at page buffer destroy time.

Tested serial/debug, serial/production, serial/check-vfd/debug,
       parallel/debug, parallel/production on Jelly.