Revert zlib.h r1.7

Revert zlib.h r1.7

The change from uLong to z_off_t was made due to a bug in gzip(1) which
was fixed by gkoehler in gzopen.c r1.35. The trouble with the z_off_t
change is that it is an ABI break and that it does not play well with
various ffi interfaces. For example, Perl and Rust break on ILP32 arches
with the system zlib.

Run through an i386 bulk by sthen and an i386 regress by bluhm, thanks.

ok bluhm