Remove yajl major version conditionals

Yajl version ≥ 2 is required.

fixes #1156
Rerender on button press only when focus changes

On button press events, the only change in state that would presently
require rerendering the tree is when the focused window changes.
fix “make dist” target

This was broken in 13db56255134a71acd2fd5a7e254adfbd0c2983b