addurl --preserve-filename: reject control characters

addurl --preserve-filename: reject control characters

As well as escape sequences, control characters seem unlikely to be desired when
doing addurl, and likely to trip someone up. So disallow them as well.

I did consider going the other way and allowing filenames with control characters
and escape sequences, since git-annex is in the process of escaping display
of all filenames. Might still be a better idea?

Also display the illegal filename git quoted when it rejects it.

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