Merged in feature/from-pantheon (pull request #16)

code from pantheon

* code from pantheon

wp/wp-content/plugins/wordpress-seo-premium/cli/cli-premium-requirement.php

@@ -0,0 +1,29 @@
+<?php
+/**
+ * WPSEO plugin file.
+ *
+ * @package WPSEO\CLI
+ */
+
+/**
+ * Enforce premium version requirement on commands covering premium features.
+ */
+final class WPSEO_CLI_Premium_Requirement {
+
+	/**
+	 * Enforces license requirements for commands representing premium
+	 * functionality.
+	 *
+	 * @return void
+	 */
+	public static function enforce() {
+		if ( YoastSEO()->helpers->product->is_premium() ) {
+			return;
+		}
+
+		// No premium commands allowed.
+		WP_CLI::error(
+			'This command can only be run with an active Yoast SEO Premium license.'
+		);
+	}
+}