Document the latest change in ENGINEs.

CHANGES

@@ -11,6 +11,11 @@
          *) applies to 0.9.6a (/0.9.6b) and 0.9.7
          +) applies to 0.9.7 only
 
+  +) Change the key loading routines for ENGINEs to use the same kind
+     callback (pem_password_cb) as all other routines that need this
+     kind of callback.
+     [Richard Levitte]
+
   *) Fix for compatibility mode trust settings: ignore trust settings
      unless some valid trust or reject settings are present.
      [Steve Henson]