Play broken if 'Display play menu tab' set to 'No'

This patch fixes an error where If you set 'Display play menu tab' to 'No' under administer > settings > video, you don't get the video. Instead you get the "?q=node/" page.

Looks like the problem was that the menu item was never getting registered for node/$nid/play. This patch changed the menu hook so that this menu hook always registers that non-cached item, and changes it to a MENU_CALLBACK if we are not showing the tab.