Instead of turning off some randomly selected http modules
when --without-http is specified, just don't process the
whole http modules section.

Some combinations of options might cause the builds with the
--with-stream option to break due to invalid value of the
STREAM_INCS make variable, e.g.

auto/configure \
    --with-stream \
    --with-http_perl_module=dynamic \
    --without-http_memcached_module \
    --without-http_empty_gif_module \
    --without-http_browser_module \
    --without-http_upstream_hash_module \
    --without-http_upstream_ip_hash_module \
    --without-http_upstream_least_conn_module \
    --without-http_upstream_keepalive_module \
    --without-http_upstream_zone_module \

Explicit initialization of ngx_module_libs and ngx_module_link
matches what we already do when processing mail modules, and
is also required after the next change.

OpenSSL 1.1.0 now uses normal "nmake; nmake install" instead of using
custom "ms\do_ms.bat" script and "ms\nt.mak" makefile.  And Configure
now requires --prefix to be absolute, and no longer derives --openssldir
from prefix (so it's specified explicitly).  Generated libraries are now
called "libcrypto.lib" and "libssl.lib" instead of "libeay32.lib"
and "ssleay32.lib".  Appropriate tests added to support both old and new
variants.

Additionally, openssl/lhash.h now triggers warning C4090 ('function' :
different 'const' qualifiers), so the warning was disabled.

In Perl 5.8.6 the default was switched to use putenv() when used as
embedded library unless "PL_use_safe_putenv = 0" is explicitly used
in the code.  Therefore, for modern versions of Perl it is no longer
necessary to restore previous environment when calling perl_destruct().

Dependencies of dynamic modules are added to NGX_ADDON_DEPS (and
it is now used for dynamic modules) to be in line with what happens
in case of static compilation.

To avoid duplication, MAIL_DEPS and STREAM_DEPS are no longer passed
to auto/module when these modules are compiled as dynamic ones.  Mail
and stream dependencies are handled explicitly via corresponding
variables.

In collaboration with Ivan Poluyanov.

IPv6 now compiled-in automatically if support is found.  If there is a need
to disable it for some reason, --with-cc-opt="-DNGX_HAVE_INET6=0" can be used
for this.