mongoreplay cannot safely terminate on one core

The pcap library (github.com/google/gopacket/pcap) locks the thread when it makes potentially-blocking CGO calls. With GOMAXPROCS set to 1 on single-core machines (or when compiled with go version <1.5), no other goroutines can run during this time, including the goroutine which listens for signals (TERM/INT/HUP). In this scenario, mongotape probably has to be closed with SIGABRT, which unsafely circumvents any end-of-program executions.