hdf5_ep

[svn-r20608] OpenVMS complainted about a test case in th5o.c which opened the same file twice.  VMS doesn't allow it.  I used the macro H5_CANNOT_OPEN_TWICE to skip the test case.  In th5s.c, I created an attribute but fogot to close it in the test case for zero dimension size.  

Tested on amani, jam.  But I haven't tested on OpenVMS yet.