Fix mamagement of UnImplemented objects in pttree.
Fix mamagement of UnImplemented objects in pttree.

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=941954.

avalentino/PyTables,avalentino/PyTables,avalentino/PyTables,FrancescAlted/PyTables,FrancescAlted/PyTables,PyTables/PyTables,PyTables/PyTables,FrancescAlted/PyTables,PyTables/PyTables