Corrected the section identifier for MySQL unicode reference.

docs/ref/unicode.txt

@@ -17,7 +17,7 @@ data. Normally, this means giving it an encoding of UTF-8 or UTF-16. If you use
 a more restrictive encoding -- for example, latin1 (iso8859-1) -- you won't be
 able to store certain characters in the database, and information will be lost.
 
-* MySQL users, refer to the `MySQL manual`_ (section 9.1.3.2 for MySQL 5.1)
+* MySQL users, refer to the `MySQL manual`_ (section 10.1.3.2 for MySQL 5.1)
   for details on how to set or alter the database character set encoding.
 
 * PostgreSQL users, refer to the `PostgreSQL manual`_ (section 22.3.2 in