PATCH: xlib double-buffering support

[Scott Gilbertson]

This is the only one of my patches that hasn't been committed.

http://gcc.gnu.org/ml/java-patches/2003-q2/msg00512.html

OK to commit (apart from making the ChangeLog entries relative to libjava
and fixing line wrap)?

It's mostly confined to the xlib peer code, but also includes changes to
gnu/awt/j2d/IntegerGraphicsState.java and java/awt/Component.java

BTW I think Graydon's stuff relies on it (see
http://gcc.gnu.org/ml/java-patches/2003-q3/msg00129.html).