We have to check both TypeError and OverflowError. On Python3 32-bit,
we'll get an OverflowError, otherwise, we get type error.

  under Python 3.

Make the Python trees and sets accept an explicit None argument to indicate an open range in keys(), values() and min/maxKey(), as per the interface documentation and the C implementation. Except actually, the C implementation didn't accept a None for mim/maxKey, so make it actually do that.

Items must be in reversed-sorted order.

Fixes #2 (maybe).

Previously, the extra required the 'ZODB3' metapackage:  depending on the
version used, the metapackage could pull in stale versions of **this**
package and 'persistent'.

I don't think we intentionally checked for Python 4.

Broeken version could contain garbage characters.

- Denominate files to indicate ReST.

- Drop .bzrignore.

Drop no-longer-used 'include'.

Note that the Python version exists only for BBB:  no application code
should instantiate one directly.