This permits compilers to check for the proper treatment of next_in and
msg in the z_stream structure. This is an option instead of the default
in order to preserve backward compatibility. Some applications make use
of the z_stream structure outside of zlib, and perform operations such
as free(strm->next_in), which would not be permitted when next_in is
const. The #define ZLIB_CONST needs to precede the #include "zlib.h">,
in order to make next_in and msg const pointers in the z_stream type.
The Microsoft CAB file format compresses each block with completed
deflate streams that depend on the sliding window history of the
previous block in order to decode. inflateResetKeep() does what
inflateReset() does, except the sliding window history from the
previous inflate operation is retained.
A common request has been the ability to compile zlib to require no
other libraries. This --solo option provides that ability. The price
is that the gz*, compress*, and uncompress functions are eliminated,
and that the user must provide memory allocation and free routines to
deflate and inflate when initializing.
This also moves some of the same from zconf.h to gzguts.h. A new
function, gzflags(), was created to pass the compilation flags
related to vsnprintf usage back to zlibCompileFlags() in zutil.c.
In the process, various compiler configuration files were updated
to include gzflags(), as well as the new gzgetc_() function added
when the gzgetc() macro was introduced in a previous patch.
