700ae685cc
(1)
Create a 1 GiB file instead of 1 TiB, because
apparently, on MacOS, the file (sometimes?) is not
created sparse, and fills up users' disks:
https://github.com/rfjakob/gocryptfs/issues/625
(2)
On darwin, SEEK_DATA is not the same as on Linux
( 2f8b555de2
)
so use the value provided by the unix package.