whether this is a correct thing to do:

+ There are linker warnings (see PCbuild\readme.txt).
+ test_bsddb passes, in both release and debug builds now.
+ test_bsddb3 has several failures, but it did before too.

Also made pythoncore a dependency of the _bsddb project, updated
build instructions, added database conversion XXX to NEWS, and fiddled
the Windows installer accordingly.