Drop all tables before restoring a PostgreSQL DB

Invoking 'db:schema:load' turned out to be a bad idea: when downgrading
an existing GitLab installation, the schema of the newer version would
be preserved when trying to import the old version.

Conflicts:
	CHANGELOG

CHANGELOG

-v6.7.2
+v 6.7.3
+  - Drop all tables before restoring a Postgres backup
+
+v 6.7.2
   - Fix upgrader script
 
 v6.7.1

lib/backup/database.rb

@@ -29,9 +29,10 @@ module Backup
         print "Restoring MySQL database #{config['database']} ... "
         system('mysql', *mysql_args, config['database'], in: db_file_name)
       when "postgresql" then
-        puts "Destructively rebuilding database schema for RAILS_ENV #{Rails.env}"
-        Rake::Task["db:schema:load"].invoke
         print "Restoring PostgreSQL database #{config['database']} ... "
+        # Drop all tables because PostgreSQL DB dumps do not contain DROP TABLE
+        # statements like MySQL.
+        Rake::Task["gitlab:db:drop_all_tables"].invoke
         pg_env
         system('psql', config['database'], '-f', db_file_name)
       end