Consolidation of the way we are handling units of measurement in XML (un)marshalling:
- Units.valueOf(String) accepts URI with #xpointer(//*[@gml:id='m']) syntax as found in ISO 19115.
- Consolidated the parsing of above URI and other syntax in a URIParser internal class.
- Remove some unit checks from internal classes, to be moved as checks done by public classes
  in the hope to produce better error messages in case of wrong or missing units.
- Unmarshall and test the unit of PrimeMeridian as a proof of concept.


git-svn-id: https://svn.apache.org/repos/asf/sis/branches/JDK7@1546824 13f79535-47bb-0310-9956-ffa450edef68