[Ada] pragma Warnings Off (str) should delete continuations

[Eric Botcazou]

> 2010-06-22  Robert Dewar  <dewar@adacore.com>
>
> 	* errout.adb (Finalize): Set Prev pointers.
> 	(Finalize): Delete continuations for deletion by warnings off(str).
> 	* erroutc.ads: Add Prev pointer to error message structure.

This apparently causes gnat.dg/not_null.adb to fail.

-- 
Eric Botcazou