Fix calling File.get_node with another file.
Fix calling File.get_node with another file.

You can call File.get_node with a Node beloging to a different file as `where`
argument. This is ok but if you also pass a `name` paramenter that name is
being looked up in the current file rather than in the file pointer by where.

This patch reworks File.get_node and fixes this behaviour.

Closes #478

gdementen/PyTables,gdementen/PyTables,mohamed-ali/PyTables,mohamed-ali/PyTables,PyTables/PyTables,FrancescAlted/PyTables,jennolsen84/PyTables,jennolsen84/PyTables,avalentino/PyTables,mohamed-ali/PyTables,joonro/PyTables,gdementen/PyTables,avalentino/PyTables,PyTables/PyTables,andreabedini/PyTables,rabernat/PyTables,rabernat/PyTables,andreabedini/PyTables,avalentino/PyTables,joonro/PyTables,FrancescAlted/PyTables,rabernat/PyTables,andreabedini/PyTables,joonro/PyTables,mohamed-ali/PyTables,jennolsen84/PyTables,FrancescAlted/PyTables,jennolsen84/PyTables,andreabedini/PyTables,PyTables/PyTables,rabernat/PyTables,joonro/PyTables,gdementen/PyTables