Allow right-click on multiple items in duplicate view. Closes #53

Originally I thought this was intentional behavior so I left it in, but now I found issue #53

I suspect that the reason this was "windows-only" bug is that right-click on mac (which IIRC historically has been Ctrl (i.e. meta) +click) triggers event.metaKey. Otherwise, the code pretty much suggests that right-click was not meant to be in duplicate view (which is why I thought it was intentional). I think it was probably also a problem on Ubuntu, but it seems that adamsmith suggests otherwise. I could be wrong though. Just my theory.