remaining fixes for LyX 1.6.4

[Uwe Stöhr]

Looking at http://www.lyx.org/trac/wiki/BugTrackerHome there are still some ugs that are fixed in 
trunk but not in branch:

- http://www.lyx.org/trac/ticket/1720
  (Maybe not ready to be backported)
- http://www.lyx.org/trac/ticket/5522
  (Richard? Jürgen gave his OK today on the list.)

- http://www.lyx.org/trac/ticket/5976

- http://www.lyx.org/trac/ticket/5998
  (Vincent?)

- http://www.lyx.org/trac/ticket/6043

regards Uwe