hdf5_chunking_query_bmr

[svn-r20064] Purpose: Implement external file cache

Description:
Implements a cache of files opened through external links.  Adds the public
functions H5Pset_elink_file_cache_size(), H5Pget_elink_file_cache_size(), and
H5Frelease_file_cache().

Tested: jam, amani, heiwa (h5committest), fedora 64.