mrd_unload - Move a cartridge from drive to slot

    Windows NT         mrd.dll
    UNIX               /usr/lib/libmrd.a
    OpenVMS            MRD$RTL.EXE

    #include <mrd_common.h>
    #include <mrd_message.h>

    int mrd_unload(
        const char   *robot_name,
        const char   *volume_tag,
        const char   *drive,
        const char   *slot,
        char         *log_info)) ;