Allow loading test-helper.el into interactive sessions
Allow hdevtool failurs on Travis CI

hdevtools can't create unix sockets on shared folders, so its tests fail
on the local Vagrant VM
Bring pkg-info require back

Without loading pkg-info our tests break, and the hassle of fixing the
tests isn't worth the effort

Revents 7d7b22b
Properly detect noninteractive sessions
Load test-helper library when editing tests

[ci skip]
Don't mock `message`

For whatever reason mocking `message` crashes Emacs.
Refactor closure-lint provisioning

Bootstrap Pip in base, and use it to install closure-lint
Update Credits and README
[Fix #245] Merge branch 'yasuyk-javascript-gjslint'

* yasuyk-javascript-gjslint:
  Update Credits and README
  Refactor closure-lint provisioning
  Add style checker for Javascript using Closure Linter
Add syntax checker for Slim using Slim compiler