Partial port of AbstractIdentifiedObject. Compared to the geotk version, we abandon the case-insensitive
search for keys in the property map. This was inefficient, made the code more complicated and appears to
be rarely needed in practice.


git-svn-id: https://svn.apache.org/repos/asf/sis/branches/JDK7@1518396 13f79535-47bb-0310-9956-ffa450edef68