Fix extension script for unpackaged upgrades to 5.2

Apparently "ALTER TABLE" (which we were using to convert the
"repl_events" table) does not mark the table as being part of the
extension. Instead, we need to create the new table and copy the
data, as is done with the other tables.

Makefile.in

@@ -12,6 +12,7 @@ EXTENSION = repmgr
 DATA = \
   repmgr--unpackaged--4.0.sql \
   repmgr--unpackaged--5.1.sql \
+  repmgr--unpackaged--5.2.sql \
   repmgr--4.0.sql \
   repmgr--4.0--4.1.sql \
   repmgr--4.1.sql \