Display a help dialog box when the user hits "?" during a diff review

Review Request #1281 — Created Nov. 30, 2009 and discarded — Latest diff uploaded

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Review Board

Reviewers

This change will allow users to get an overview of keyboard shortcuts while users are reviewing changes.  It includes the ThickBox javascript code (MIT licensed).  Please let me know if this is not OK.

Hussain Bohra should be listed as a contributor if this code is accepted.  Thanks!
Manual testing on a development box at tip + diffs (as of last week).