which calls generic WillInsert, DidInsert to test for magic bogus
content and does the right thing.
You now can't delete magic content with user gestures, and when you
insert anything the magic kludgy is deleted first.
attribute MOZ_EDITOR_BOGUS_NODE set to TRUE. this solves the problem of when you do a SelectAll then a DEL, you don't have a cursor
or any way to set selection in the document. You do still have the problem that the nbsp is pretty narrow and the frame containing it is hard to hit
with the mouse. We really need the "set selection to frame nearest the mouse down point" operation.
the intent is for all inserts to look for this node, and if found delete it before the insert. likewise, all deletes will be no-ops if this node is found.
