title: Xcode 4 Cmd+alt+up/down remapping
body: <p>I realise that switching between header and implementation files has moved to ctrl+cmd+up/down.</p>
  
  <p>however this is incredibly annoying, as there is no Ctrl button near the arrow keys, before I could do it quickly with 3 fingers on one hand. </p>
  
  <p>So i opened up preferences found that I could change the key bindings and attempted to press cmd+alt+up/down. However it seems that it is the only box that refuses to accept the alt key. I tried any combination of alt+any key, and it just entered the key without alt. How can I bypass this? Is there a manual way of setting key bindings, and why on earth is alt not allowed in these 2 particular key bindings?</p>