[merge] Allow '-' as an argument

[Martin Pool]

On 11 Jul 2006, John Arbash Meinel <john at arbash-meinel.com> wrote:
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> https://launchpad.net/products/bzr/+bug/50984
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> The current argument parsing code borks if you do:
> 
> bzr command -
> 
> Because it starts to think it is a short option, but has no argument.
> At present, no commands support '-' (for say reading from stdin). But
> the argument parser should support it. Especially so that plugins can
> support reading from stdin. (And in the future bzr merge/bzr pull should
> probably allow bundles to be piped in for cat bundle | bzr merge -, but
> that is not done yet).
> 
> The attached patch just adds a test that '-' is valid as a command line
> argument, and gets parsed as an argument rather than an option.

+1, though I thought we already fixed this.

-- 
Martin