Fix valueWriterFn_ variable name

This change will help us separate binary support into
separate files, because we only refer to binary serialization
functions in the actual binary serialization paths.

A couple of small tweaks were needed to fix test failures that were
inadvertently introduced in the last down integration. I also had to add
the map.js file which was missing.

This includes all internal changes from around May 20 to now.

The runtime doesn't depend on anything, so these
packages should always have been in devDependencies.

Varints are generally encoded in minimum possible length but need to
ensure that any redundancy does not break fields decoder.

"nodejs" does not exist on Travis, it appears.