title: Missing link between objectContribution and command
body: <p>When using the <code>objectContribution</code>-element (which is part of the <a href="http://help.eclipse.org/helios/topic/org.eclipse.platform.doc.isv/guide/workbench_basicext_popupMenus.htm" rel="nofollow"><code>org.eclipse.ui.popupMenus</code></a>-extension point), I often (practically always) want to delegate to some command instead of  implementing some action myself (since usually, I have the command and a handler already implemented). I'm doing this by using <code>ICommandService</code> and <code>IHandlerService</code>, but it feels there should be a way to achieve this programmatically. I could use <code>viewerContribution</code> instead of <code>objectContribution</code>, but then I would lose the easy way of showing the menu entry only when certain object types are selected. Ideally, I would like to use the enablement-checks that already exist for my handlers to apply to the menu entry defined by the <code>objectContribution</code>.</p>