linuxcnctop: fix the crawling scrollbar in many cases

.. by only changing the necessary part of the text, the 'crawl' is usually
avoided.  It might still occur in cases when a changing value is one that
is split across more than two lines (at least this is the pattern I
believed I saw when working on this problem).

It looks and smells like a Tk bug but oh well
Merge branch 'v2.5_branch' into 2.6
pickconfig: speed automatic closing of other branches

By deferring the treeclose/treeopen until idle, the work isn't done
each time a single tree node is opened/closed.  Doing this work
repeatedly (with included "update" command) caused the automatic closing
to take an appreciable amount of time, particularly on slower machines.