hdf5_msb

[svn-r16477] Purpose: Fix problem with opening an attribute multiple times through multiple
file handles.

Description:
An attribute's "oloc" field which specifies the file it resides in was located
in the attribute's "shared" structure.  So when an attribute was opened multiple
times all of the handles for that attribute pointed to the same file id, even if
different file id's were used to open the different handles for the attribute.
The "oloc" has been moved to the top level H5A_t struct.

Tested: jam, smirom (h5committest)