hdf5_ep

[svn-r14086] Description:
    Correct error in metadata cache entry logic for free space objects, where
a free space header could unpin its entry in the cache, even when the sections
for that free space manager were still in the cache and technically holding the
header pinned.  Fix problem by checking for the section info in the cache
before allowing the header to unpin its cache entry.

Tested on:
    FreeBSD/32 6.2 (duty)
    Mac OS X/32 10.4.10 (amazon)
    Linux/32 2.6 (chicago)
    Linux/64 2.6 (chicago2)