This is a working version of the zlib version 1.2.4 but there are still some
rough edges that needs to be improved. Specifically:

• zlib now uses off_t instead of long. So far I am fairly confident that this *should* work just fine but still needs further testing, etc.
• The change from long to off_t requires users to rebuild all their binaries if linked with zlib. (Should we avoid the shared library version bump?)
• We diveraged a little bit from official zlib's definition for their 64-bit variants. Technically we should have all these stuff without the 64 prefix since our off_t is 64 bit from the day 0 of FreeBSD 2.x, which is derived from 4.4BSD-Lite, while version 7.21 92/05/13 14:44:26 mckusick bumped it to 64-bit. Currently this is done with some direct changes in zlib.h and hack in zconf.h.
• We need to import zlib's versioned symbols, perhaps the same of Linux's one provided with the distribution, or our own (since we bumped shared library version).