Make D-Bus properties type safe

Make D-Bus properties type safe

* doc/misc/dbus.texi (Properties and Annotations):
Precise dbus-get-property and dbus-set-property.
(Type Conversion): Explain :byte and :boolean type conversion.
(Errors and Events): dbus-ignore-errors returns nil when there is
a D-Bus error.  Remove dbus-show-dbus-errors.

* etc/NEWS: Some D-Bus relevant changes.

* lisp/net/dbus.el (dbus-show-dbus-errors): Remove.
(dbus-ignore-errors): Replay implamentation without that variable.
(dbus-check-arguments): New defun.
(dbus-list-activatable-names, dbus-list-names)
(dbus-list-queued-owners, dbus-get-name-owner, dbus-introspect)
(dbus-get-all-properties, dbus-get-all-managed-objects): Don't debug.
(dbus-get-property, dbus-set-property): Propagate errors.
(dbus-register-property): Check for valid VALUE.
(dbus-property-handler): Simplify.

* src/dbusbind.c (Fdbus_message_internal): Adapt docstring.
Handle DBUS_MESSAGE_TYPE_INVALID.

* test/lisp/net/dbus-tests.el (dbus-show-dbus-errors): Don't declare.
(dbus-test06-register-property)
(dbus-test06-register-property-emits-signal): Adapt tests.