Sets the uninstallation hook for a plugin.

Registers the uninstall hook that will be called when the user clicks on the
uninstall link that calls for the plugin to uninstall itself. The link won’t
be active unless the plugin hooks into the action.

The plugin should not run arbitrary code outside of functions, when
registering the uninstall hook. In order to run using the hook, the plugin
will have to be included, which means that any code laying outside of a
function will be run during the uninstallation process. The plugin should not
hinder the uninstallation process.

If the plugin can not be written without running code within the plugin, then
the plugin should create a file named ‘uninstall.php’ in the base plugin
folder. This file will be called, if it exists, during the uninstallation process
bypassing the uninstall hook. The plugin, when using the ‘uninstall.php’
should always check for the ‘WP_UNINSTALL_PLUGIN’ constant, before
executing.

function register_uninstall_hook( $file, $callback ) {
	if ( is_array( $callback ) && is_object( $callback[0] ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Only a static class method or function can be used in an uninstall hook.' ), '3.1.0' );
		return;
	}

	/*
	 * The option should not be autoloaded, because it is not needed in most
	 * cases. Emphasis should be put on using the 'uninstall.php' way of
	 * uninstalling the plugin.
	 */
	$uninstallable_plugins = (array) get_option( 'uninstall_plugins' );
	$plugin_basename       = plugin_basename( $file );

	if ( ! isset( $uninstallable_plugins[ $plugin_basename ] ) || $uninstallable_plugins[ $plugin_basename ] !== $callback ) {
		$uninstallable_plugins[ $plugin_basename ] = $callback;
		update_option( 'uninstall_plugins', $uninstallable_plugins );
	}
}