Prevent pg_basebackup -Fp -D -?

Right now, if you use

pg_basebackup -Ft -D -

you get a tarfile, written to stdout, for redirection.

However, if you use:

pg_basebackup -Fp -D -

you get a plaintext (unpackaged) backup, in a directory called "-".

I can't think of a single usecase where this is a good idea. Therefor,
I would suggest we simply throw an error in this case, instead of
creating the directory. Only for the specific case of specifying
exactly "-" as a directory.

Comments?

Also, if we do that, is this something we should consider
backpatchable? It's not strictly speaking a bugfix, but I'd say it
fixes some seriously annoying behavior.

--
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/