review request (S): 7199082 write warning messages to stderr

[John Coomes]

Small change to warning() to write to error_stream() instead of tty.

http://cr.openjdk.java.net/~jcoomes/7199082-warn-stderr/

Bug link:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7199082

-John