CBLT-159:  SYNCGATE_VERSION now edition-specific

Change-Id: I201adb6c5bd0a2996b40a709de60105d86fac4a6
Reviewed-on: http://review.couchbase.org/37916
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>