[bp/r53270][FIX]  forums: Some mail clients place font and span tags as invalid list elements causing HTMLPurifier to remove the list completely so remove them first

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/12.x@53271 b456876b-0849-0410-b77d-98878d47e9d5