Adds a 'type' attribute to the 'dependency' tag, with possible values
'required' and 'optional'.
Optional dependencies may not be linked against. You'll need to use the
new dynamic methods in plugin manager (retrieving objects and calling
methods by name) if you want to access functionality of optional
dependencies.
If a plugin requests asyncronous shutdown, the shutdown sequence does
not continue to deleting the plugins before it has sent a
asynchronousShutdownFinished signal. During that time an event loop
is running.
The noload behavior is also changed: it now always shows the plugins in
About Plugins... menu, even though -noload was used. When using -noload,
the enabled state of the plugin is not saved, so if the command line
arg is removed, the plugin will be loaded normally.
Reviewed-by: con
