Hook for plugin activation/initial setup

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I propose a hook for activating a plugin. The hook would be called whenever a plugin is activated, with the name (or possibly filename) of the plugin as its argument. A plugin could then know it has just been activated, and take any initial setup steps it needs to take to configure itself without user intervention, or possibly to redirect the user to the plugin's options if necessary. (Spam Karma 2 needs this, for instance.)

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hm, this code's already in wp-admin/plugins.php. sorry!