Limit the number of open connections in a server

[GoogleCodeExporter]

I'm following some discussions about HTTP/2 and a new WSGI design (see web-sig) 
and one issue brought up (pretty randomly) is that async frameworks typically 
don't let you limit how many incoming connections a server can have open at any 
time.  Thinking about load balancers it's pretty clear that this would be a 
useful feature to have in the framework: it's hard to implement this in the 
application, because it doesn't get control over the accept() syscall.

Original issue reported on code.google.com by [email protected] on 16 Oct 2014 at 3:55