Bug 126414 [Commands] handlers: Provide help context ids
For commands and handlers to replace actions, they need to be capable of providing help context identifiers. For an example, see OpenResourceHandler in org.eclipse.ui.ide. This help context id will need to be definable through XML and through code.
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/Command.java
buffer.append("') has changed to "); 
			if (handler == null) {
				buffer.append("no handler"); 
			} else {
				buffer.append('\'');
				buffer.append(handler);
				buffer.append("' as its handler"); 
			}
			Tracing.printTrace("HANDLERS", buffer.toString()); 
		}
		
		fireCommandChanged(new CommandEvent(this, false, false, false, true,
				false, false, false));
		return true;
	}
	/**
	 * The string representation of this command -- for debugging purposes only.
	 * This string should not be shown to an end user.
	 * 
	 * @return The string representation; never <code>null</code>.
	 */
	public final String toString() {
		if (string == null) {
			final StringBuffer stringBuffer = new StringBuffer();
			stringBuffer.append("Command("); 
			stringBuffer.append(id);
			stringBuffer.append(',');
			stringBuffer.append(name);
			stringBuffer.append(',');
			stringBuffer.append(description);