non ne sono sicuro ma penso basti metterla senza il punto e virgola davanti ...prova

codice:
;;;;;;;;;;;;;;;;;;;;;;
; Dynamic Extensions ;
;;;;;;;;;;;;;;;;;;;;;;
;
; If you wish to have an extension loaded automatically, use the following
; syntax:
;
;   extension=modulename.extension
;
; For example:
;
;   extension=msql.so
;
; Note that it should be the name of the module only; no directory information 
; needs to go here.  Specify the location of the extension with the
; extension_dir directive above.
extension=mysql.so 

;;;;
; Note: packaged extension modules are now loaded via the .ini files
; found in the directory /etc/php.d; these are loaded by default.
;;;;