Check for DIRECTORY_SEPARATOR

Based on fix from @nuessgens at wpengine#201

Author: greatquux

src/wpephpcompat.php

@@ -464,6 +464,10 @@ public function clean_after_scan() {
 	 * @return null
 	 */
 	private function add_directory( $name, $path ) {
+		if (DIRECTORY_SEPARATOR == '\\') {
+    			$path = str_replace("\\","/", $path);
+    		}
+
 		$dir = array(
 			'post_title'   => $name,
 			'post_content' => $path,