ticket:11029: Added some note about methods not yet implemented. Also updated these method to do nothing but returns DONE.

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@36410 251d0590-4201-4cf1-90de-194747b24ca1
ticket:7118: document that compare() is often more efficient than getSortKey()

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@36414 251d0590-4201-4cf1-90de-194747b24ca1
ticket:11249 BRS 54: Verify malloc functions fix to class NFDIterator.

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@36421 251d0590-4201-4cf1-90de-194747b24ca1