Use DOM interfaces to implement XML operators

Sun's Java 1.5.0 and higher includes Xalan, but Derby doesn't find it because it has been moved to a non-standard package. Derby should be able to detect and use these classes if it cannot find Xalan in the standard package on the classpath. This would make it easier for many users to start using Derby's XML features.

See also the discussion in this thread: <URL:http://mail-archives.apache.org/mod_mbox/db-derby-dev/200705.mbox/%3c465F015C.9070404@gmail.com%3e>