Alberto Miranda authored Feb 22, 2020 and Marc Vef committed Apr 24, 2020

Also, remove outdated import.

lseek was triggering a number overflow by converting long to integer on
its return value

Added specific lseek test

All the relevant env variables are now prefixed with GKFS instead of
ADAFS

`adafs_preload_client` -> `gkfs_intercept`

`adafs_daemon` -> `gkfs_daemon`