early alpha of D REPL

[thedeemon]

> Have you seen Dabble?
> https://github.com/callumenator/dabble

Just found out its author added Linux support. I was able to 
build an x86 version but it didn't work properly in a 64 bit 
system: it assumes dmd makes x86 binaries by default while it 
really makes 64-bit ones. And for 64 bits Dabble doesn't compile: 
as it often happens, it's too easy to forget that array.length is 
not always uint.