hdf5_der

[svn-r24805] Rework of metadata cache logging.

- Functionality separated out into a separate set of functions.
- Log format is now based on JSON.
- Logging does not require a recompile.
- Added new H5F/H5P log control functions.

- Also fixed an error in Makefile.am that wasn't building some
  flush_prevent test programs from being built.

Tested on: jam