Bug 148357 [Field Assist] - API - provide access for closing the proposal popup
I think that the field assist API needs more hooks to be customizable. For example : 1) There is no way to manually close/open the popup. Most of the times, this is the easier thing for a user to ask to implement his custom behaviour. 2) There is no way to intercept keystrokes/events directed to the field. 3) There is no way to control focus.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ContentProposalAdapter.java
*            an instance which is already registered with this instance,
	 *            this method has no effect.
	 * 
	 * @see org.eclipse.jface.fieldassist.IContentProposalListener
	 */
	public void addContentProposalListener(IContentProposalListener listener) {
		proposalListeners.add(listener);
	}
	/*
	 * Add our listener to the control. Debug information to be left in until
	 * this support is stable on all platforms.
	 */
	private void addControlListener(Control control) {
		if (DEBUG) {
			System.out
					.println("ContentProposalListener#installControlListener()"); 
		}
		if (controlListener != null) {
			return;
		}
		controlListener = new Listener() {
			public void handleEvent(Event e) {
				if (!isEnabled) {
					return;
				}
				switch (e.type) {
				case SWT.Traverse:
				case SWT.KeyDown:
					if (DEBUG) {
						StringBuffer sb;