ticket:10128: add support for UBA 6.3 isolates

git-svn-id: http://source.icu-project.org/repos/icu/icu@33851 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10128: add support for UBA 6.3 isolates. Fix obsolete comments.

git-svn-id: http://source.icu-project.org/repos/icu/icu@33852 251d0590-4201-4cf1-90de-194747b24ca1