Csaba/"Jester" and /me: since a few weeks the property browser had

Csaba/"Jester" and /me: since a few weeks the property browser had
displayed garbage in the title line if one left a directory. Jester
spent a lot of time finding the cause: a bug that must have been
there since ... forever: fgfs reported to PUI the string addresses
as returned by SGPropertyNode::getStringValue() without considering
that this address isn't valid after the next write access to that
node! It's almost a miracle that it worked so well for so long,
despite that issue. (I also used to opportunity for some more
cleanup -- so I'm to blame for any newly introduced bugs, and
also for reverting some of Jester's cleanups. :-)