Use golang.org/x/sys/windows for FileLockEx/UnlockFileEx
Use golang.org/x/sys/windows for FileLockEx/UnlockFileEx

Use the FileLockEx and UnlockFileEx wrappers and the corresponding
LOCKFILE_* and the ERROR_LOCK_VIOLATION error constants from the
golang.org/x/sys/windows package rather than implementing these in the
package.

etcd-io/bbolt