limit_rate based on proxy upstream response header

[Rob Mueller]

> It's expected, as rewrite directives (including "set" and "if")
> are exectured during rewrite phase, i.e. before request to backend
> happens.

I thought it might be something like that.

> Try returning X-Accel-Limit-Rate header instead.  Not sure it's
> documented somewhere except in source code, but it's at least
> mentioned here:
>
> http://wiki.nginx.org/NginxXSendfile

Excellent, that worked thanks.

I've updated the NginxHttpCoreModule in the limit_rate section to make a 
note of that.

http://wiki.nginx.org/NginxHttpCoreModule

Rob