[opus] Get server headers.

[Timothy B. Terriberry]

alpha thinktink wrote:
> Is it possible to get the HTTP server headers for URL streams opened
> with op_open_url, op_vopen_url?  If not, is there an alternative that I
> can use get get the headers?

There isn't. This gets complicated by the fact that for redirects or 
proxy connections, there may be multiple sets of headers per request, 
and for seekable streams there may be lots of requests, each with their 
own set of headers. The library also destructively modifies these 
headers during parsing.

What information do you need from them?