2.1.3 has very few improvements over 2.1.2, but the most important
are some thread-safety fixes that were causing heavily loaded Zope
sites to keel over.
Major changes:
- no more threads flavor, threads is now the default.
- subpackage modules that depend on other packages instead of having
largely redundant flavors (unless platform has no shared libs, then
flavors count again)
- shared libpython stuff disabled until someone can figure out why
it makes Zope crash