Per attribute value open should be renamed

[greenTara]

Change the name of the attribute on "per" from "open" to "request".
The old name should still be valid in the relaxed serialization for backward compatibility.

• Relax NG Schemas - change content model of per attribute, add the old name to the module that maintains backward compatibility.
• Unit Tests - add some test examples using the new name.
• XSLT -

Dependent on Issue #38