Support interactive D-Bus authorization

Support interactive D-Bus authorization

When invoking D-Bus methods, let the user enable interactive
authorization by passing an :authorizable t parameter.  This makes
it possible to D-Bus methods that require polkit authorization.

* configure.ac (HAVE_DBUS_MESSAGE_SET_ALLOW_INTERACTIVE_AUTHORIZATION):
Set a new variable if `dbus_message_set_allow_interactive_authorization'
is available.

* src/dbusbind.c (dbus-message-internal): Allow interactive
authorization by passing :authorizable t.

* doc/misc/dbus.texi (Synchronous Methods, Asynchronous Methods):
* etc/NEWS:
* lisp/net/dbus.el (dbus-call-method-asynchronously): Document the
new parameter.

(cherry picked from commit 551a71c313be26d067e59fa11c79e4ef5c550e92)