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.