Check if value of NO_COMPRESSION/NO_ZLIB is 0 or 1.
Originally, only presence of these variables was checked.
Unfortunately, iostreams documentation said, incorrectly,
that NO_ZLIB and NO_BZIP2 default to 1 on Windows, which
caused some users to pass NO_ZLIB=0 explicitly, together
with other variables,thereby still disabling zlib.
This match makes Jamfile forgiving of this error.
Fixes #1967.
[SVN r52168]
Vladimir Prus