keyring, update_version, ... compatible with 4.7

[Marcin Kasperski]

I just tested my extensions ( https://mekk.bitbucket.io/mercurial.html )
against Mercurial 4.7, and released versions which fix various
incompatibilities (especially keyring, update_version, and
extension_utils, really had to be patched).

So if you see some crashes after switching to 4.7, please upgrade
them.

~~~~~~~~~~~~~~

In case some other extension writer is yet to take a look, I mostly
faced those two incompatibilities:

- various mercurial.util.* functions disappeared (and live now in
  mercurial.utils.stringutil, mercurial.utils.dateutil etc)

- demandimport.ignore list is gone, replaced by SET demandimport.IGNORES