unlockpt - remove lock from master/slave pseudoterminal pair

Syntax	#include <stdlib.h> int unlockpt (int fildes);
Description	The unlockpt() function unlocks the slave pseudoterminal associated with the master pseudoterminal specified in fildes. Portable applications must call unlockpt() before they open the slave side of a pseudoterminal device.
Return val.	0 -1	if successful. otherwise. errno is set to indicate the error.
Errors	unlockpt() will fail if:
	EBADF	The fildes argument is not a file descriptor open for writing.
	EINVAL	The fildes argument is not assigned to a master pseudoterminal.
See also	grantpt(), open(), ptsname(), stdlib.h.