ads-github-fetch-all-upstreams: only one unprocessed named repo noted in error message

[salewski]

This issue pertains to the ads-github-fetch-all-upstreams tool from
'ads-github-tools' version 0.1.1, and is an improvement for the fix
implemented for issue #1.

When a user fat-fingers more than one repo name on the command line,the
program prints an error message that names only the first unprocessed repo
name that is detected.

It would be more useful if the program were to name all unprocessed repo names
because that both gives a better indication to the user about the size of the
error, and also gives the user the opportunity to correct all such errors at
once (rather than playing whack-a-mole fixing one at a time and having
successive runs of the program fail on the remaining repos that were not named
in the error message).

Here's an example of the current 0.1.1 behavior:

    $ ads-github-fetch-all-upstreams --version | head -n 1
    ads-github-fetch-all-upstreams 0.1.1  (built: 2016-09-27 17:49:46)

    $ ads-github-fetch-all-upstreams bogon-repo1 bogon-repo2 bogon-repo3
    ads-github-fetch-all-upstreams (error): did not process explicitly requested repo: "bogon-repo1"; bailing out