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.
The bsddb subproject is gone.
The _bsddb subproject is new.
There are problems here, but I'm out of time to work on this now. If
anyone can address an XXX comment or two in readme.txt, please do!