This reduces the number of moving parts in ABI compatibility checks.
Additionally, it also allows to use OpenSSL in FIPS mode while still
using md5 for non-security tasks.

The auto/module script is extended to understand ngx_module_link=DYNAMIC.
When set, it links the module as a shared object rather than statically
into nginx binary.  The module can later be loaded using the "load_module"
directive.

New auto/module parameter ngx_module_order allows to define module loading
order in complex cases.  By default the order is set based on ngx_module_type.

3rd party modules can be compiled dynamically using the --add-dynamic-module
configure option, which will preset ngx_module_link to "DYNAMIC" before
calling the module config script.

Win32 support is rudimentary, and only works when using MinGW gcc (which
is able to handle exports/imports automatically).

In collaboration with Ruslan Ermilov.

Splits a request into subrequests, each providing a specific range of response.
The variable "$slice_range" must be used to set subrequest range and proper
cache key.  The directive "slice" sets slice size.

The following example splits requests into 1-megabyte cacheable subrequests.

server {
    listen 8000;

    location / {
        slice 1m;

        proxy_cache cache;
        proxy_cache_key $uri$is_args$args$slice_range;
        proxy_set_header Range $slice_range;
        proxy_cache_valid 200 206 1h;
        proxy_pass http://127.0.0.1:9000;
    }
}

The SPDY support is removed, as it's incompatible with the new module.

stream {
    limit_conn_zone $binary_remote_addr zone=perip:1m;
    limit_conn_log_level error;

    server {
        ...
        limit_conn perip 1;
    }
}

It's now initialized in auto/options like the rest of variables
for system paths.

As a side effect, the currently unused macro NGX_SBIN_PATH now
gets the correct value.