Bug 627993 - Inconsistent storage of password expiry times
    
    Commit made in 5727b8899700f574026bc9be5a1990c4c66619cf introduced
    a bug.  The commit removed 2 functions format_genTime and
    parse_genTime from slapi-private.h.  But they are used in plugins,
    which requires them in the header file.  This fix restores the
    function declarations.