Extensions, patch v18 (merge against master, bitrot-only-fixes)

Hi,

Well $subject says about it all really. The bitrot of course comes from
the fact that the last in-commitfest-dependency has been commited in,
and I kept a version of pg_execute_sql_file() in the extension's patch.

Following the discussions, and as exposing this function is not
necessary for CREATE EXTENSION to work as needed, it's not exposed at
the SQL level anymore.

Please note that the SQL scripts seem to be encoded in latin9. I don't
think there's a policy about that already, and I'd like to get
confirmation about that before to go ahead and add encoding = latin9 to
the control files.  Whatever the master sources encoding policy is, I
think explicitely marking it in the control files will be a good idea.

Regards,
-- 
Dimitri Fontaine
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support