Refs http://stackoverflow.com/questions/9762943
The system ln no longer outputs anything. Though the user can force its output with a --verbose of course. So in cases where it's not the usual of: not writable or existing file, we can ask the user to run with --verbose. I don't particularly like hiding its output, but it just confused the error IMO since it is creating a relative symlink the output was weird every time I've seen it in tickets.
I made a print wrapper so that the brew-link output doesn't get mucked up if an exception is thrown.
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