To avoid further breaks it's now done properly, all the dependencies
are now passed to Makefile.PL.  While here, fixed include list passed to
Makefile.PL to use Makefile variables rather than a list expanded during
configure.

It's no longer necessary to update src/http/modules/perl/nginx.pm
when version is bumped, as it's now derived from src/core/nginx.h.

Filename extension used for dynamically loaded perl modules isn't
necessarily ".so" (e.g., it's ".bundle" on Mac OS X).

This fixes "make" after "make" unnecessarily rebuilding perl module.

Added missing dependencies for perl module's Makefile.

Simplified dependencies for perl module nginx.so: it depends
on Makefile that in turn depends on other perl bits.

No functional changes.

Note: the "-p" argument of cp(1) dropped intentionally, to force nginx.so
rebuild.  It is considered too boring to properly list all dependencies
in Makefile.PL.

When using IPv6 databases, IPv4 addresses are looked up as IPv4-mapped
IPv6 addresses.

Mostly based on a patch by Gregor Kališnik (ticket #250).

This was introduced for conditional compilation of the code that requires
the zlib library.