Use syscall.TIOCGPTN and syscall.TIOCSPTLCK for ioctl

Signed-off-by: Yohei Ueda <yohei@jp.ibm.com>
Remove ioctl_* constants on Linux

Signed-off-by: Yohei Ueda <yohei@jp.ibm.com>
Remove uintptr(...)

Signed-off-by: Yohei Ueda <yohei@jp.ibm.com>
Merge pull request #26 from yoheiueda/use-syscall-consts

Use syscall.TIOCGPTN and syscall.TIOCSPTLCK for ioctl