hdf5_ep

[svn-r18396] Purpose: Fix links.c failure

Description:
The core file driver previously matched files only based on the name used to
open them, even when a backing store is used.  This caused problems in the
failing test when it traversed an external link to itself, and did not recognize
that it was the same file.  Similar tests in links.c were skipped when the core
file driver was used.  The failure was previously masked by inappropriate file
flushes caused by external link traversal.  Added code to the core file driver
to keep track of low level file information of the backings store to allow for
accurate recognition of duplicate files.  Also re-enabled all links.c tests for
the core file driver.

Tested: Fedora (core and sec2 drivers; no time for full commit test, will
monitor daily tests)