Aesthetics in GenTrees.

A nominee for "worst textual shape" might be

  \\\\\
  /////
  \\\\\
  /////
  \\\\\
  /////

where the zigzagging wall of text is confined to the
first forty columns. In this commit we halve the vertical
space usage and double the readability.
Aesthetics in Trees.

As long as it's a block of pure boilerplate we have to
navigate around all the time, it may as well be the most
beautiful boilerplate it knows how to be.
Merge pull request #3036 from paulp/pr/aesthetics

Improvement in code aesthetics.