'Get the filepath\'s owner\'s group.  If this is not implemented
(say in Windows) return the string "0" since stat-ing a file in
Windows seems to return C{st_gid=0}.
(Reference:
U{http://stackoverflow.com/questions/5275731/os-stat-on-windows})
@param fp: L{twisted.python.filepath.FilePath}
@return: C{str} representing the owner\'s group'

def _stat_group(self, fp):

    try:
        groupID = fp.getGroupID()
    except NotImplementedError:
        return '0'
    else:
        if (grp is not None):
            try:
                return grp.getgrgid(groupID)[0]
            except KeyError:
                pass
        return str(groupID)
