When windowBits is zero, the size of the sliding window comes from
the zlib header.  The allowed values of the four-bit field are
0..7, but when windowBits is zero, values greater than 7 are
permitted and acted upon, resulting in large, mostly unused memory
allocations.  This fix rejects such invalid zlib headers.

A remarkably creative and diverse set of approaches to letting the
compiler know that opaque was being used when it wasn't is changed
by this commit to the more standard (void)opaque.

The C standard says that bit shifts of negative integers is
undefined.  This casts to unsigned values to assure a known
result.

This is in order to permit shared memory for these structures.

To build, simply run configure from the source directory by
specifying its path.  That path will be used to find the source
files.  The source directory will not be touched.  All new and
modified files will be made in the current directory.  Discovered
in the process that not all makes understand % or $<, and not all
compilers understand -include or -I-.  This required a larger
Makefile.in with explicit dependencies.

Sun compiler complained.  Use (unsigned)0 - 1 instead.

This updates the documentation to reflect the behavior of
deflateParams() when it is not able to compress all of the input
data provided so far due to insufficient output space.  It also
assures that data provided is compressed before the parameter
changes, even if at the beginning of the stream.

It previously could have been misinterpreted to mean that parameter
changes after deflateInit2() would be reversed, which is not the
case.

A windowBits value of 0, 16, or 32 gets the window bits from the
zlib header.  However there is no zlib header for 16, or for 32
when the input is gzip.  This commit sets the window bits for
inflate to 15 if a gzip stream is detected and windowBits was 16
or 32.

Previously there was a confusing reference to a "distribution
directory".

The C standard permits an undefined result for a left shift of a
negative value.

An open() with O_APPEND followed by an lseek() to determine the
position will return zero for a non-empty file, even though the
next write will start at the end of the file.  This commit works
around that by doing an lseek() to the end when appending.

to report the count of unused bytes at the end correctly.  Add the
ability to provide initial input to blast().

Forcing Z_CONST resulted in an issue when compiling Firefox.  Now
if someone wants to compile zlib as C++ code (which it isn't), now
they will need to #define Z_CONST themselves.