Install deps of compat-table to avoid make clean installs.

With git dev-dependences in package.json, the dependencies of that dependent
seem to be reinstalled every time we run `npm install`; we run `npm install` every time we
run `make clean`. To avoid these downloads on `make clean` we install the recursive dependencies
directly.
Switch to kangax repo.
Fixes #1178

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1184

Closes #1184, closes #1178.
Fix regression of free var checker in accessors

With the recent change to the new ScopeVisitor a "typo" sneaked in
preventing us from visiting the body of accessors.