#90 Editing _ContentBaseDefinition can crash IIS

[Anonymous]

If you change the Namespace property in
_ContentBaseDefinition to a namespace which does not
exist, any requests to the wiki, or it seems, any other
pages on the webserver fail till the connection timeouts
or the server is rebooted.

This is a very serious issue, since it lets people sabotage
an entire server with very little effort.