Please allow zlib_tpu into testing

[Mark Brown <broonie@sirena.org.uk>]

The version of zlib in testing currently lacks the last round of
security fixes to the library.  As well as fixing the security issues
this would also avoid confusion on the part of users upgrading from
stable who often find that they can't install the -dev package due to
already having the security fix version of the library.

There is an updated version in unstable but it has been constantly held
up by a range of issues (currently it is held back by glibc).

-- 
"You grabbed my hand and we fell into it, like a daydream - or a fever."