refactorings for Set and Stream, removed ReadOnlyIterator

git-svn-id: http://highj.googlecode.com/svn@166 bdcd8b68-9dcc-aa74-f1b9-b4da3e61a8cc
corrected Set.equals and Set.hasCode (can't rely on iteration order because of buckets)

git-svn-id: http://highj.googlecode.com/svn@167 bdcd8b68-9dcc-aa74-f1b9-b4da3e61a8cc