[PATCH] cli: try to run external notmuch- prefixed commands as subcommands

[David Bremner]

Jani Nikula <jani at nikula.org> writes:

> If the given subcommand is not known to notmuch, try to execute
> external notmuch-<subcommand> instead. This allows users to have their
> own notmuch related tools be run via the notmuch command, not unlike
> git does. Also notmuch-emacs-mua will be executable via 'notmuch
> emacs-mua'.
>
> By design, this does not allow notmuch's own subcommands to be
> overriden using external commands.

pushed to master