Message 75494 - Python tracker

Here's an updated patch, with the following changes from the original:

- make the size of a digit (both the conceptual size
in bits and actual size in bytes) available to Python
via a new structseq sys.int_info.  This information
is useful for the sys.getsizeof tests.

- fix a missing cast in long_hash

- better fast path for 1-by-1 multiplication that
doesn't go via PyLong_FromLongLong.