Ticket #27196: 27196.2.diff

src/wp-admin/includes/class-wp-upgrader.php

@@ -52 +52 @@
                 $this->strings['installing_package'] = __('Installing the latest version…');
                 $this->strings['no_files'] = __('The package contains no files.');
                 $this->strings['folder_exists'] = __('Destination folder already exists.');
+                $this->strings['remove_first'] = __( 'Unable to install over existing folder - you probably need either to delete the installed version first, or to perform your update using the dashboard\'s updates page.' );
                 $this->strings['mkdir_failed'] = __('Could not create directory.');
                 $this->strings['incompatible_archive'] = __('The package could not be installed.');
 
@@ -364 +365 @@
                 $this->skin->set_result($result);
                 if ( is_wp_error($result) ) {
                         $this->skin->error($result);
+                        if ( in_array( 'folder_exists', $result->get_error_codes() ) ){
+                                $this->skin->feedback( 'remove_first' );
+                        }
                         $this->skin->feedback('process_failed');
                 } else {
                         //Install Succeeded