1) Added code test/page_buffer.c to verify that page buffering is
disabled in parallel builds.
2) Added code to test/cache_image.c to verify correct interaction
between evict on close and cache image -- in particular management
of a file containing a cache image containing dirty metadata that
has been opened R/O. Also fix for the bug exposed.
3) Added code to testpar/t_cache_image.c to verify expected procedure
for reading cache images, and also supporting stats collection code
needed for the test.
4) Repair of an overactive sanity check in H5C__reconstruct_cache_contents().
5) Other minor tidies in passing.
Tested serial and parallel, debug and production on Jelly.
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.
