Bug 250133 [Contexts] ContextAction's leak when hiding actions sets
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/contexts/ContextManager.java
*            <code>null</code>.
	 */
	public final void removeActiveContext(final String contextId) {
		if (!activeContextIds.contains(contextId)) {
			return;
		}
		activeContextsChange = true;
		if (caching) {
			activeContextIds.remove(contextId);
		} else {
			final Set previouslyActiveContextIds = new HashSet(activeContextIds);
			activeContextIds.remove(contextId);
			fireContextManagerChanged(new ContextManagerEvent(this, null,
					false, true, previouslyActiveContextIds));
		}
		if (DEBUG) {
			Tracing.printTrace("CONTEXTS", activeContextIds.toString()); 
		}
	}
	/**
	 * Removes a listener from this context manager.
	 * 
	 * @param listener
	 *            The listener to be removed; must not be <code>null</code>.
	 */
	public final void removeContextManagerListener(
			final IContextManagerListener listener) {
		removeListenerObject(listener);
	}
	/**