Make to call post_copy in postgres.CopyToTable.copy

[woojing]

It seems just missing. so I filling.

[Tarrasch]

Somebody knowing postgres should review this :)

[dlstadther]

LGTM. (Except that your second commit is meaningless here - needs rebase.)

I am the one who included the post_copy for rdbms and redshift. I also set up redshift to accept an optional property queries such that the post_copy method was already implemented. However, it is up to you whether you want to do the same/similar within postgres.py or if you want to leave it up to the user to implement their own post_copy().