Typos from Covering Index patch

Hi all,

I am catching up with new features so I have begun going through
Covering indexes.  While reading the code, I have noticed a couple of
things:
1) Some typos.
2) An inconsistent variable name in pg_dump.

The thing and structure of the code is pretty interesting by the way.
That's nice work.  I am still trying to break the DDL data like
NULL-ness of columns for some weird combinations of columns without
being able to.

Thanks,
--
Michael