guys had to change the name to differentiate with older versions when
a backward incompatibility came up.  Of course, we need to adapt.
This change simply tries to load the library through the newer name
(ZLIB1) first, and if that fails, it tries the good old ZLIB.

let's wrap it with a lock.

and provide missing prototypes.

stateless variant is kept, but isn't used anywhere.

only the first call would provide the correct result.
PR: 277

missed any.

This compiles and runs on Linux, and external applications have no
problems with it.  The definite test will be to build this on VMS.

systems where such an operation is supported.

Windows.  Really, this should probably be done on Unix as well, but
that will be a later story...

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PR: