Hi Peter,
I had the same problem this morning and then saw your message.
I used 'ldd' to see what libraries the svn client uses, and
then looked at which ones changed when I updated yesterday.
Then I backed off one package at a time until the problem
went away.
My client works again after downgrading libneon27-gnutls.
Edit your '/etc/apt/preferences' and add this:
-------------------------------------------
Package: libneon27-gnutls
Pin: release o=Debian,a=stable
Pin-Priority: 1001
-------------------------------------------
Then run 'sudo apt-get install libneon27-gnutls'. It should
downgrade the package.
Bad version: libneon27-gnutls (0.28.4-1)
Good version: libneon27-gnutls (0.28.2-6.1)
-Brad