DIP19: Remove comma operator from D and provision better syntactic support for tuples

[Andrei Alexandrescu]

I discussed this with Walter, and we concluded that we could deprecate 
the comma operator if it helps tuples. So I started with this:

http://www.prowiki.org/wiki4d/wiki.cgi?LanguageDevel/DIPs/DIP19

Unfortunately, I started much cockier than I ended. The analysis in 
there fails to construct a case even half strong that deprecating the 
comma operator could significantly help tuples. Well it essentially 
concludes that tuples are mostly fine as they are, and attempts to 
embellish them syntactically are marred with unexpected problems. 
Nevertheless, I sure have missed aspects all over, so contributions are 
appreciated.


Thanks,

Andrei