Re: [PATCH v2 1/1] remote-curl: unbreak http.extraHeader with custom allocators

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> In 93b980e58f5 (http: use xmalloc with cURL, 2019-08-15), we started to
> ask cURL to use `xmalloc()`, and if compiled with nedmalloc, that means
> implicitly a different allocator than the system one.
>
> Which means that all of cURL's allocations and releases now _need_ to
> use that allocator.
>
> However, the `http_options()` function used `slist_append()` to add any
> configured extra HTTP header(s) _before_ asking cURL to use `xmalloc()`,
> and `http_cleanup()` would release them _afterwards_, i.e. in the
> presence of custom allocators, cURL would attempt to use the wrong
> allocator to release the memory.

> A naïve attempt at fixing this would move the call to
> `curl_global_init()` _before_ the config is parsed (i.e. before that
> call to `slist_append()`).
>
> However, that does work, as we _also_ parse the config setting

> `http.sslbackend` and if found, call `curl_global_sslset()` which *must*
> be called before `curl_global_init()`, for details see:
> https://curl.haxx.se/libcurl/c/curl_global_sslset.html
>
> So let's instead make the config parsing entirely independent from
> cURL's data structures. Incidentally, this deletes two more lines than
> it introduces, which is nice.