public MessageBox

[Nathan M. Swan]

After playing around with making a library with uses threads, I 
realized it would be nice if there could be multiple inter-thread 
mailboxes than just one per thread. That way, client code and 
third-party library code don't interfere with each other.

So this is my proposal: that std.concurrency is modified so that 
class MessageBox is public and MessageBoxs be passed around 
through other MessageBoxs, or perhaps another class is devised 
for this.

I'm not sure of the implications of this, though I know I would 
find it very useful by allowing me to write code without ("import 
core."~someLowLevelModule)