Note to third party packagers on zlib dependency for Bazaar 2.2

[Martin (gzlist)]

Bazaar 2.2 no longer needs to zlib header files to build any pyrex
extensions, and does not need to link against zlib directly. Instead,
it uses the Python zlib module. This simply means bzr no longer needs
to directly depend on a zlib package, depending on python is
sufficient. The 2.2b3 source package contains the change if you wish
to test prior to the final release.

Martin