auto-detect changes in OPatch releases

Use newest release of OPatch whenever it is available.  The newest should be marked with <access> Open access</access>

<patch has_prereqs="n" has_postreqs="n" is_system_patch="n">
<bug>
<name>28186730</name>
<type>Patch</type>
<status>Available</status>
<access id="m">Open access</access>