Disallow functions named "and", "or", or "not".

Closes #1265
Fix deprecation warning File.exists? -> File.exist?
Update ruby patch version

https://www.ruby-lang.org/en/news/2014/05/09/ruby-2-1-2-is-released/
Stop skipping Ruby 2.1 on Travis.

The outstanding bug has been fixed as of 2.1.2.
Merge remote-tracking branch 'origin/stable' into stable
Merge branch 'ruby-2-1-2' into stable

Closes #1272
Merge remote-tracking branch 'origin/stable' into stable
Merge branch 'stable' into fix-deprecation-warning-file-existsp
Add a changelog entry for File.exists?
Merge branch 'fix-deprecation-warning-file-existsp' into stable

Closes #1286