obsolete ALI files

[Nicolas Boulenguez <nicolas.boulenguez@free.fr>]

Hello.

My explanation was wrong, there is a new victim (libaws).

However, if recompiling libraries and packages without changing ALI
versions in Build-Dependencies removes the error, then a library
somewhere is probably breaking the Ada policy by silently changing the
contents of its Ada sources.

--- gnat-6_6.0.1-1/usr/lib/gcc/*/6/adainclude/a-textio.adb
+++ gnat-6_6.1.1-4/usr/lib/gcc/*/6/adainclude/a-textio.adb
@@ -668,7 +668,7 @@
             Available := True;

             Item :=
-              (if Is_Start_Of_Encoding (Character'Val (ch), File.WC_Method)
+              (if not Is_Start_Of_Encoding (Character'Val (ch), File.WC_Method)
                then Character'Val (ch)
                else
             Get_Upper_Half_Char_Immed (Character'Val (ch), File));
          end if;

I suggest that:
We ask a rebuild of every package/architecture built using ALI files
older than this change, by topological order of Build-Dependencies of
course.
We do not bother updating ALI versions. I may be wrong, but I think it
is too late for this to be useful.