Previously the fact that some configuration options were only stored
in the database (and thus editing the config file had no effect) was a
source of user confusion. This was fixed with the series ending at
d9af0af164.
On the other hand, the underlying partition of config options into
those stored by default in the database and those stored in the config
file remained. This is also confusing, since now some invocations of
"notmuch config set" modify the config file, and others silently
modify the database instead.
With this commit, it is up to the user to decide which configuration
to modify. A new "--database" option is provided for notmuch config to
enable modifying the configuration information in the database;
otherwise the default is to update an external config file.
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.
