I updated httpclient to 4.2.6; this depends on core 4.2.5 (there is no
later 4.2 release) so did not update that.

At some point we should probably move to 4.3 for both.
However the 4.3 release has deprecated a lot of classes and methods,
so it is not a drop-in replacement.

Also it looks like the post/put details have changed slighty - I got
compare failures from the tests when I tried 4.3 initally. I suppose
it's possible that this was a consequence of not having fixed the
deprecation errors (though that seems a bit unlikely).

It would probably be sensible to try and resolve the POST/PUT errors
before fixing the deprecations in case there are problems migrating.