Wraps send(), sending string ``s`` to child process, with os.linesep
        automatically appended. Returns number of bytes written.

def sendline(self, s=''):
        '''Wraps send(), sending string ``s`` to child process, with os.linesep
        automatically appended. Returns number of bytes written. '''

        n = self.send(s)
        return n + self.send(self.linesep)