minor: travis.yml should install enterprise-server package

We don't need the tools or the shell from the meta package so installing
them just wastes time.
CXX-237 Add support for merging bulk write results
CXX-164 Become agnostic about boost thread version
CXX-238 Enforce update/replace bulk semantics
CXX-164 Fix windows build breakage introduced in d43d275

The object to join is the thread, not the notification.
minor: add current symlink for docs