remove reference to non-existent class
fix location of EC2 latent build slave
fix module name
make ec2 not to bail when boto is not installed

* however make it bail if EC2LatentBuildSlave is used anyway
Update waterfall view
Merge tothandras/buildbot:waterfall_view (PR #1191)
Merge sa2ajj/buildbot:fix-misc-latent-slave (PR #1190)
remove tests for absence of dateutil (it's required now)