Basic unwrapping in 2.5

I tried creating a mesh, entering edit mode, selecting all the vertexes, unwrapping, and looking at the UV editor. I expect to see an unwrapped mesh, but nothing is visible in the UV editor. Now what?

Go into edit mode then either
Select all the vertices in the mesh
In the UV/Image editor header select the button with the tooltip “Keep UV and edit mode mesh selection in sync”

No such button is present. Here’s what I see:

Press the X to unview the “Render Result” image.

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