backporting features to D1

[Walter Bright]

Derek Parnell wrote:
> Another problem was trying to have the same codebase support both D1 and D2
> - that makes it filled with the silly string mixin workaround, which is
> plain butt ugly.

I understand that's a problem. I don't think that solving it is 
compatible with the goal of separate lexing, parsing, and semantic 
analysis passes. That leaves a couple of options:

1. What I do is have two separate code bases for D1 and D2 code, and use 
the unix program "meld" to manually do a merge now and then. meld makes 
this quick and easy. I also use meld to help keep the compiler sources 
in sync.

2. Use an external text processing facility to generate the two source 
code versions. This is what I do with the D documentation - they use 
Ddoc macros to generate each custom version.