Throw an exception if node size is negative (Fixes #259).
Throw an exception if node size is negative (Fixes #259).

svn path=/trunk/libavg/; revision=6566

yyd01245/libavg,th3infinity/libavg,libavg/libavg,scotty007/libavg,hoodie/libavg,scotty007/libavg,hoodie/libavg,th3infinity/libavg,th3infinity/libavg,libavg/libavg,yyd01245/libavg,scotty007/libavg,yyd01245/libavg,scotty007/libavg,libavg/libavg,th3infinity/libavg,yyd01245/libavg,libavg/libavg,hoodie/libavg,hoodie/libavg