Since the provider should now build everywhere,
enable it inconditionally to catch minor problems

As a replacement, added appropriate operator [] functions.  All other uses can
use getStr().

From an email conversation with Stephen Bergmann

"I think the real intent always was to actually look through all the
returned getSuperclasses(), and the error that superclasses past the
first one are effectively ignored has never been noticed."

When exporting to xls, we weren't encoding the so-called virtual paths
(used for recording external workbook paths etc) correctly when the
external docs were located under the same drive as the referencing doc.
This patch fixes this.