Add ON UPDATE / ON DELETE CASCADE clause for the powa_extensions FK.

Thanks to Andriy Bartash for the report.

powa--4.1.1--4.1.2.sql

@@ -1,2 +1,7 @@
 -- complain if script is sourced in psql, rather than via CREATE EXTENSION
 --\echo Use "ALTER EXTENSION powa" to load this file. \quit
+
+ALTER TABLE public.powa_extensions DROP CONSTRAINT powa_extensions_srvid_fkey;
+ALTER TABLE public.powa_extensions ADD
+    FOREIGN KEY (srvid) REFERENCES public.powa_servers (id)
+    MATCH FULL ON UPDATE CASCADE ON DELETE CASCADE;

powa--4.1.2.sql

@@ -979,6 +979,7 @@ CREATE TABLE public.powa_extensions (
     version text,
     PRIMARY KEY (srvid, extname),
     FOREIGN KEY (srvid) REFERENCES public.powa_servers (id)
+      MATCH FULL ON UPDATE CASCADE ON DELETE CASCADE
 );
 
 INSERT INTO public.powa_extensions(srvid, extname) VALUES