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.
afd8f64c29