I18N: Use the actual placeholder instead of a number in translator comments if the corresponding string does not use numbered placeholders.

Add missing translator comments in `WP_Theme_Install_List_Table` and `wp_notify_postauthor()`.
Add missing commas in some translator comments.

Fixes #43523.
Built from https://develop.svn.wordpress.org/trunk@42827


git-svn-id: http://core.svn.wordpress.org/trunk@42657 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-http-curl.php

@@ -190,7 +190,7 @@ class WP_Http_Curl {
 			if ( ! $this->stream_handle ) {
 				return new WP_Error(
 					'http_request_failed', sprintf(
-						/* translators: 1: fopen() 2: file name */
+						/* translators: 1: fopen(), 2: file name */
 						__( 'Could not open handle for %1$s to %2$s.' ),
 						'fopen()',
 						$r['filename']