I modified the Xdmf reader to return a single multi-block grid in the
case of a collection where the collection type was unset and in the case
of a tree. I also modified it to set the time in the case of a single
time state. This resolves #557.



git-svn-id: http://visit.ilight.com/svn/visit/trunk/src@13495 18c085ea-50e0-402c-830e-de6fd14e8384