hdf5_ep

[svn-r16710] Purpose: Fix bug 1423

Description:
Versions of the library between 1.3.0 and 1.6.3 have a bug which prevents them
from opening any file that does not have the root group's symbol table
information cached in the root group's entry in the superblock.  Prior to 1.8
this was not an issue as this information was always cached.  However, 1.8.0
stopped writing this information (which is not required by the file format
specification), and these older versions can therefore not read files created or
last written by versions 1.8.0 to 1.8.2.  This fix modifies the library to once
again add this information to the superblock (when using the old file format).

Tested: jam, linew, smirom (h5committest)