Old erlang vms don't have ErlDrvSSizeT

Change-Id: I19d0c9d41adc01c7548beebd63b520aa19134afe
Reviewed-on: http://review.couchbase.org/34877
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>