...when SwCntntNode::DelFrms is called from ~SwTxtNode -> ~SwCntntNode.

* SwCntntNode::DelFrms now needs a flag to distinguish calls from inside
  ~SwCntntNode from other calls.  bIsDisposeAccTable happens to already serve
  that purpose, so I reused it, but that may be a bad idea from a semantic point
  of view?

* ~SwTxtNode is careful to mimic old behavior and only calls DelFrms_TxtNodePart
  if GetDepends() is true; no idea whether that's really necessary, though.

* Shifting the work done by DelFrms_TxtNodePart from within ~SwCntntNode to
  before ~SwTxtNode calls ~SwCntntNode hopefully has no negative consequences.

Change-Id: I1532b4cfef7fbf9ba82e64b919a08cbefa335421