Since we are already passing a search context around as a kind of
parameter block, add a new talloc context to that to replace relying
on 'config'.
Convert notmuch-search and notmuch-address at the same time, because
they share some code.
Add a test to make sure we don't break passing configuration as a
command line argument.
These restrictions are meant to prevent incompatibilities with the
Xapian query parser (which will split at non-word characters) and
clashes with future notmuch builtin fields.
We don't do anything with this configuration information information
yet, but nonetheless add a couple of regression tests to make sure we
don't break standard functionality when we do use the configuration
information.
