Kill implicit joining of adjacent strings

[Walter Bright]

Andrei Alexandrescu wrote:
> Let me ask a related question: if there were a priority list of things 
> that Walter should be busy with, where would this feature be on that list?

For once, I agree with Bearophile. The adjacent string concatenation was a very 
very early feature, and the ~ completely supplants it. While I don't think it 
causes many problems, it's a pointless redundancy and should be removed.