Pluggable auth modules

[Pavel Strashkin]

Hello DBusers,

At the moment DBus has a few hard-coded auth mechanism and there is no
the way to fix them separately, extend, inherit or add a new one
without a patching.

Actually, an adding a new one is a more complicated problem because
you can't just add it to main repo - it must be approved by dbus team
or it's may be your own
proprietary (or for internal usage) code so the only way is keep this
patches under your control and merge/refresh them everytime when
mainstream is changed (sometimes it's difficult).

The idea is introduce pluggable auth modules (DLO, dynamically
loadable objects) via *.so/*.dll which will contain some factory
function to produce DBusAuthMechanismHandler instances.
What do you think?

Thank you!