Improve diff view: spaces and underscores

[slel]

This diff:

https://ncatlab.org/nlab/revision/diff/Alexander+Grothendieck/35

has two problems:

• it shows the underscore before _Récoltes and _Reminiscences
  (when it should not)
• it eats the space between "of" and "Sasha" (in the line
  that has the change Reminiscenes -> Reminiscences)