dirname() is a slow function compared with __DIR__ and using
'/../'. Moodle has a large number of legacy files that are included
each time a page loads and is not able to use an autoloader as it is
functional code. This allows those required includes to perform as
best as possible in this situation.
The admin setting updateautodeploy no longer exists. The two existing
config.php flags $CFG->disableupdateautodeploy and
$CFG->disableonclickaddoninstall merged into a single one.
Most of the functionality provided by this tool (typically the
validation and actual deployment of the plugin package) has been moved
to the core level. So this is becoming just a thin wrapper and user
interface for installing new plugins via the administration UI.
Also fixes MDL-49600 as we no longer keep the unzipped contents of the
packages in the persistent temp directories.
Brendan Heywood