C++ Binding: changes for version 1.0b

The following changes were made between versions 1.0a and 1.0b of the ZOOM C++ binding:

1. Added forward declarations for the classes Z3950_search, Z3950_resultSet and Z3950_record.

The sole purpose of these changes was to make the header file into syntactically legitimate C++, and so allow compilation of the following totally trivial test code:

#include <stddef.h>
#include "current.hh"
int x = 0;