e107inc#5209: Add full-text indexes to table comments

`e107_handlers/search/search_comment.php` hasn't been migrated to
e107 v2 standards yet, so we forgot to add indexes of the search
fields specified here:
https://github.com/e107inc/e107/blob/a3c04d6b1dcf5593462863bd4a80c5f2d809f2f1/e107_handlers/search/search_comment.php#L67

e107_core/sql/core_sql.php

@@ -103,7 +103,9 @@
   comment_share tinyint(1) unsigned NOT NULL default '0',
   PRIMARY KEY  (comment_id),
   KEY comment_blocked (comment_blocked),
-  KEY comment_author_id (comment_author_id) 
+  KEY comment_author_id (comment_author_id),
+  FULLTEXT (comment_comment),
+  FULLTEXT (comment_author_name)
 ) ENGINE=InnoDB;
 # --------------------------------------------------------