overage is guaranteed over all pixels included in either of
the arguments, ie more pixels may be covered than the "exact"
union.</P
><P
>Note: this routine is used in the Gnome Canvas to accumulate the
region that needs to be repainted. However, since it copies over
the entire uta (which might be largish) even when the update may be
small, it can be a performance bottleneck. There are two approaches
to this problem, both of which are probably worthwhile. First, the
generated uta's should always be limited t