mostly so I can valgrind both and make sure they free all their
workspace - a memory leak in this code would be not merely an
inconvenience but a security hazard.
[originally from svn r9101]
testdata/bignum.py is twice the size of the rest of the PuTTY source
put together, so I'm not checking it in.
This reveals bugs in the new multiplication code, which I have yet to
fix.
[originally from svn r9097]