Can't use plain numbers as HTML attributes

(Bug, To be Fixed , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
QText
Summary: The specific case where this came up was for tables: you can't say <td colspan=4> -- it doesn't pass the whitelisting in BaseParsers.scala::xmlAttrVal
This is only High because you can work around it by putting quotes around the number.