operations like deleteTHead, deleteTableCell etc., could frequently leak nodes 
as removeChild would never drop refcount to 0 (just setParent). This changes it to do 
so; and just the users that need node kept alive to do so. Note tha this also means these
ops no longer return the old node, as it's not guaranteed to be alive...

Prerequisite for making some latter work sane...

svn path=/branches/KDE/3.5/kdelibs/; revision=583314