Detect the V8 api

Change-Id: Ib9c784d98489e83020de57c6d096f8ede132f424
Reviewed-on: http://review.couchbase.org/32865
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>