Change the comment to a more appropriate one. Discussed with Heikki on IM.

Approved by:	Heikki

include/dict0mem.h

@@ -158,12 +158,13 @@ struct dict_col_struct{
 					of an index */
 };
 
-/* DICT_MAX_INDEX_COL_LEN is measured in bytes and is the max index column
-length + 1. Starting from 4.1.6, we set it to < 3 * 256, so that one can
-create a column prefix index on 255 characters of a TEXT field also in the
-UTF-8 charset. In that charset, a character may take at most 3 bytes.
-This constant MUST NOT BE CHANGED, or the compatibility of InnoDB data files
-would be at risk! */
+/* DICT_MAX_INDEX_COL_LEN is measured in bytes and is the maximum
+indexed column length (or indexed prefix length). It is set to 3*256,
+so that one can create a column prefix index on 256 characters of a
+TEXT or VARCHAR column also in the UTF-8 charset. In that charset,
+a character may take at most 3 bytes.
+This constant MUST NOT BE CHANGED, or the compatibility of InnoDB data
+files would be at risk! */
 
 #define DICT_MAX_INDEX_COL_LEN		768