Version bump.
SSL: loading certificate keys via ENGINE_load_private_key().
Cache: send conditional requests only for cached 200/206 responses.

RFC7232 says:

   The 304 (Not Modified) status code indicates that a conditional GET
   or HEAD request has been received and would have resulted in a 200
   (OK) response if it were not for the fact that the condition
   evaluated to false.

which means that there is no reason to send requests with "If-None-Match"
and/or "If-Modified-Since" headers for responses cached with other status
codes.

Also, sending conditional requests for responses cached with other status
codes could result in a strange behavior, e.g. upstream server returning
304 Not Modified for cached 404 Not Found responses, etc.

Signed-off-by: Piotr Sikora <piotr@cloudflare.com>
Proxy: the "TE" header now stripped by default (ticket #537).
Upstream: inheritance of proxy_pass and friends (ticket #645).

Instead of independant inheritance of conf->upstream.upstream (proxy_pass
without variables) and conf->proxy_lengths (proxy_pass with variables)
we now test them both and inherit only if neither is set.  Additionally,
SSL context is also inherited only in this case now.

Based on the patch by Alexey Radkov.
Upstream: fixed unexpected inheritance into limit_except blocks.

The proxy_pass directive and other handlers are not expected to be inherited
into nested locations, but there is a special code to inherit upstream
handlers into limit_except blocks, as well as a configuration into if{}
blocks.  This caused incorrect behaviour in configurations with nested
locations and limit_except blocks, like this:

    location / {
        proxy_pass http://u;

        location /inner/ {
            # no proxy_pass here

            limit_except GET {
                # nothing
            }
        }
    }

In such a configuration the limit_except block inside "location /inner/"
unexpectedly used proxy_pass defined in "location /", while it shouldn't.
Fix is to avoid inheritance of conf->upstream.upstream (and
conf->proxy_lengths) into locations which don't have noname flag.
Proxy: fixed incorrect URI change due to if (ticket #86).

In the following configuration request was sent to a backend without
URI changed to '/' due to if:

    location /proxy-pass-uri {
        proxy_pass http://127.0.0.1:8080/;

        set $true 1;

        if ($true) {
            # nothing
        }
    }

Fix is to inherit conf->location from the location where proxy_pass was
configured, much like it's done with conf->vars.