Add build-time version check for libcouchbase

This makes the compilation message a bit friendlier, rather than showing
garbage about undefined structures.

Change-Id: Ic9d7f329d2e8d668afa3b9b092b17985a071f3d9
Reviewed-on: http://review.couchbase.org/29285
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>