Small changes for the "no excuses" release

PostgreSQL seem to have a lot of names;
Postgres 95, Postgres, Pg, Pgsql ... All these names are used in
FAQ, filenames, docs, installation info, messages etc.

Examples:
The backend executable is 'postgres', why not 'postgresql'?
INSTALL: "User postgres is the Postgres superuser"?

I think it would be a good idea to use only "PostgreSQL" in all
docs, file names and so on, and "pgsql" as the official abbrev.

This is one of the things new users notice and find strange.
I know, because I did, and people I know did it too.

Another strange thing is the name "postmaster". Someone doing a 'ps'
seeing this would probably think it is part of the email system.
A better way would be to use 'postgresql' only, or perhaps with a
'--master' option.

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