hdf5_ep

[svn-r19005] Purpose:

    Commit metadata tagging framework.

Description:

    This check-in contains a new framework whose goal is to apply
    a tag value to each new entry in the metadata cache as it is created. 
    This tag value is such that it relates each piece of metadata to the 
    HDF5 object that it belongs to (dataset, group, et cetera).

    This changeset includes the framework that applies the tags as 
    well as a suite of tests to verify correct tag application, though does
    not yet make use of the tag values to flush/evict individual objects.

    Please refer to the "flush/evict individual objects" RFC for further
    discussion of these changes.

Tested:

    jam, amani, linew (h5committest)
    liberty, abe, blue print