#2 Help file cannot be openned more than once

[Gary Feng]

The current version of TeView uses the Wikit as Help
manager. However, if one opens and closes the help
wikit, and opens it again, there will be an error
complaining that "help.()..." undefined or something
like that.

I suspect the function is cleared when Wikit exists.
Need to figure this out, but low priority.

Work around: quit and restart the editor.