Multiple selection support (r480) breaks plugin API and Hamster plugin

The plugin api's get_selected_task() method uses a function that doesn't work when the treeview is set to allow multiple selection.

The answer is to have the function call the browser's get_selected_task() method instead. We should probably also expose get_selected_tasks() so plugins can take advantage of multiple selection (though it's not useful for hamster).

I thought it was that simple, but ...
Is there a reason the PluginAPI doesn't hold a reference to the browser object, just to a bunch of its components? I wonder what other plugin API methods are already implemented in the browser or could be simplified by being able to use browser methods.

Traceback (most recent call last):
  File "/home/km/temporary/gtg/trunk/GTG/plugins/hamster/hamster.py", line 199, in browser_cb
    self.sendTask(plugin_api.get_selected_task())
  File "/home/km/temporary/gtg/trunk/GTG/core/plugins/api.py", line 312, in get_selected_task
    model, iter = selected.get_selected()
TypeError: GtkTreeSelection.get_selected can not be used when selection mode is gtk.SELECTION_MULTIPLE