* Use Lyx-Code more extensively. Do not use begin/end_deeper
* Better postASP support for non verbatim in tscreen.

    We want to support things like

    <tscreen><verb>
    I am a <tt/verbatim/ line
    </verb>
    I am not a <tt/verbatim/ line
    </tscreen>

  Since nsgmls will break lines when look changing commands are found in
  tscreen+non-verbatim, we need to make sure that LyX-Code commands are
  not sent neither during the look change nor in the line after it. No
  problem in verbatim+tscreen, since lines will not be broken.

  We use $inlookchange to signal this, 0 or undefined means no look change,
  1 means in look change and 2 means last line ended a look change.