toString refactor in druntime

[Kagamin via Digitalmars-d]

On Thursday, 30 October 2014 at 15:32:30 UTC, Steven 
Schveighoffer wrote:
> This would require sink to write the buffer before it's first 
> call, since you don't track that.

Also not always true, depends on sink implementation. If you 
construct string in memory, you can concat the buffered result 
with sunken result any time later.