zlib options

[Taylor R Campbell <campbell%mumble.net@localhost>]

Last month I submitted a PR, now fixed thanks to Jeremy Reed, for
enabling zlib support in OpenSSL.  I looked a little further, and
found a number of packages that have zlib-related options.  There is
no option named `zlib' in mk/defaults/options.description; there are
options `bzip2', `gzip', and `lzw'; and lang/clisp and net/rbldnsd
also have a `zlib' option.  There is also a `links-zlib' option used
only by www/links, and there are three options `unrealircd-ziplinks',
`inspircd-ziplinks', and `ziplinks' used by different IRC server
packages that enable zlib.  Finally, www/lighttpd has a `bzip' option
that enables support for bzip2, which is misleading.

I don't know the conventions governing the naming of these options,
and whether they suggest distinguishing `support for a library X'
(e.g., zlib) from `support for functionality that happens to depend on
a library X' (e.g., ziplinks), but this collection of options seems
somewhat inconsistent, and if nothing else it would be nice for the
`zlib' option to be documented.