hdf5_ep

[svn-r17177] In H5Odtype.c, the decoding function used to mark the datatype as on disk (see bug 
#1585).  I changed it to undefined and let the caller functions decide the location 
of the datatype.  For H5Tdecode, it should mark the datatype as in memory.  For other 
callers like H5Dopen or H5Aopen, they should makr it as on disk.

Tested it on jam, smirom, linew.