[feature/attachment-management-no-reassignment] Further feature adjustments.

-add database update entry;
- add files statistics checks;
- improve files deletion procedure;
- improve reversed order for pagination;
- adjust template file;
- add missing comma for orphan key in info module;
- change module mode name;
- fix module explanation text;
- add files comments output;
- change attachments per page amount from posts to topics per page value.

PHPBB3-9721

phpBB/language/en/acp/common.php

@@ -118,7 +118,7 @@ $lang = array_merge($lang, array(
 	'ACP_MAIN'					=> 'ACP index',
 
 	'ACP_MANAGE_ATTACHMENTS'			=> 'Manage attachments',
-	'ACP_MANAGE_ATTACHMENTS_EXPLAIN'	=> 'Here you can manage files attached to posts. You are able to delete the files or reassign them to existing posts. Reassigning to posts requires a valid post ID, you have to determine this ID by yourself. This will reassign the already assigned attachment to the post you entered.',
+	'ACP_MANAGE_ATTACHMENTS_EXPLAIN'	=> 'Here you can list and delete files attached to posts and private messages.',
 
 	'ACP_MANAGE_EXTENSIONS'		=> 'Manage extensions',
 	'ACP_MANAGE_FORUMS'			=> 'Manage forums',
@@ -238,6 +238,9 @@ $lang = array_merge($lang, array(
 	'EXPORT_DOWNLOAD'		=> 'Download',
 	'EXPORT_STORE'			=> 'Store',
 
+	'FILES_GONE'			=> 'Some of the attachments you selected for deletion do not exist. They may have been already deleted. Attachments that did exist were deleted.',
+	'FILES_STAT_WRONG'		=> 'Your files statistics is probably inaccurate and might need to be resynchronised. Actual values: number of attachments » %1$d, total size of attachments » %2$s.',
+
 	'GENERAL_OPTIONS'		=> 'General options',
 	'GENERAL_SETTINGS'		=> 'General settings',
 	'GLOBAL_MASK'			=> 'Global permission mask',
@@ -263,6 +266,7 @@ $lang = array_merge($lang, array(
 	'NOTIFY'				=> 'Notification',
 	'NO_ADMIN'				=> 'You are not authorised to administer this board.',
 	'NO_EMAILS_DEFINED'		=> 'No valid e-mail addresses found.',
+	'NO_FILES_TO_DELETE'	=> 'Attachments you selected for deletion do not exist.',
 	'NO_PASSWORD_SUPPLIED'	=> 'You need to enter your password to access the Administration Control Panel.',
 
 	'OFF'					=> 'Off',