pg_comparator support for PostgreSQL 9.4

[Sebastiaan Couwenberg <sebastic@xs4all.nl>]

Hi Ivan,

In response to #757960 I took the liberty of looking into updating
pg_comparator for PostgreSQL 9.4.

pg_comparator builds fine with its build dependency changed to
postgresql-server-dev-all as suggested in the BTS.

lintian reported some typos which I also took the liberty to fix and
forward upstream.

Is there something you'd like to include in the next upload of
pg_comparator or shall I do a team upload of the changes I commit in git?

Kind Regards,

Bas

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