[O] Bug (?) in new exporter (export subtree)

[Rick Frankel]

In the new exporter, when the option to export only the subtree is
specified, the first heading in the subtree is used as the title of
the document. This seems wrong, as it becomes the title, the first
element in the table of contents and the first (not necessarily
the top level) section in the document.

When the document is explicitly narrowed to the subtree, or the
subtree is the selected region, the #+Title: attribute is used for the
document title, which seems to be better.

Arguably, using the subtree heading for the title would be the most
logical solution when exporting a subtree -- in my case that would
usually DWIM.

rick