MDL-26854 COMMENT

1. added pluginname_comment_validate callback to comments api
2. change permission callback defaults to false
3. Tidied up serveal areas of comments and implemented callback to
ignore system permissions for view (credits to Sam Hemelryk)

AMOS BEGIN
    MOV [modulerejectcomment,error],[callbackrejectcomment,error]
AMOS END

mod/data/lang/en/data.php

@@ -62,6 +62,7 @@ $string['commentempty'] = 'Comment was empty';
 $string['comments'] = 'Comments';
 $string['commentsaved'] = 'Comment saved';
 $string['commentsn'] = '{$a} comment(s)';
+$string['commentsoff'] = 'Comments feature is not enabled';
 $string['configenablerssfeeds'] = 'This switch will enable the possibility of RSS feeds for all databases. You will still need to turn feeds on manually in the settings for each database.';
 $string['confirmdeletefield'] = 'You are about to delete this field, are you sure?';
 $string['confirmdeleterecord'] = 'Are you sure you want to delete this entry?';