Add libevent and cURL as dependencies

Change-Id: I5c340ea7b5b7fd31479a8e1be5f895fbc35c05a8
Reviewed-on: http://review.couchbase.org/29294
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>