trailing whitespace in psql table output

Everyone using git diff in color mode will already or soon be aware that
psql, for what I can only think is an implementation oversight, produces
trailing whitespace in the table headers, like this:

 two |     f1     $
-----+------------$
     | asdfghjkl;$
     | d34aaasdf$
(2 rows)$

($ is the line end; cf. cat -A).  Note that this only applies to
headers, not content cells.

Attached is a patch to fix that.