Updated ScrollPane with boundary checking.
Updated ScrollPane with boundary checking.

	* libraries/javalib/java/awt/ScrollPane.java
	(ScrollPane): supports GraphicsEnvironment.isHeadless() checks.
	(addImpl): checks scrollbar type.
	(getScrollPosition), (getViewportSize), (layout), (layoutX):
	scrollbar boundary check.

kaffe/kaffe,kaffe/kaffe,kaffe/kaffe,kaffe/kaffe,kaffe/kaffe