Fix #5552: add clue to error log when flash is unavailable after server

restart without session persistence

impl/src/main/resources/com/sun/faces/LogStrings.properties

@@ -119,7 +119,7 @@ faces.config.legacy.facelet.warning=JSF1029:  Application is versioned at 2.0 (e
 faces.view.cannot.render.response.committed=JSF1030: Unable to render view ''{0}'' as the response has already been committed.
 faces.compcomp.unecessary.targets.attribute=JSF1092: {0} : Unnecessary specification of the ''targets'' attribute for composite attribute ''{1}''.  The ''targets'' attribute is only necessary when the composite attribute is named ''action'', ''actionListener'', ''validator'', or ''valueChangeListener''.
 faces.compcomp.binding.eval.non.compcomp=JSF1093: {0} : UIComponent returned by expression evaluation is not a valid composite component.  Value will be ignored.
-faces.externalcontext.flash.bad.cookie=JSF1094: Could not decode flash data from incoming cookie value {0}.  Processing will continue, but the flash is unavailable for this request.
+faces.externalcontext.flash.bad.cookie=JSF1094: Could not decode flash data from incoming cookie value {0}.  Processing will continue, but the flash is unavailable for this request.  Most probably server was restarted without session persistence.  One solution is to set java:comp/env/faces/FlashSecretKey with a fixed AES256 key. 
 faces.externalcontext.flash.response.already.committed=JSF1095: The response was already committed by the time we tried to set the outgoing cookie for the flash.  Any values stored to the flash will not be available on the next request.
 faces.metadata.uiviewroot.unavailable=JSF1096: UIViewRoot unavailable at the time view metadata was being processed.  Metadata will be unavailable.
 faces.application.resource.invalid_if_modified_since_header=JSF1097: Unable to parse date sent by User Agent for If-Modified-Since header, {0}.