Run release builds on Travis
Run release builds on Travis

(Also, don't manually build the tests before running them. We were
doing so inconsistently anyway, and the important point is to build
NodaTime first so we see any issues there early.)

nodatime/nodatime,BenJenkinson/nodatime,malcolmr/nodatime,malcolmr/nodatime,malcolmr/nodatime,BenJenkinson/nodatime,nodatime/nodatime,jskeet/nodatime,malcolmr/nodatime,jskeet/nodatime