Added Hole Horizontal Expansion setting.

[smartavionics]

Provide simple solution for #2158.

[rburema]

I'm going to merge this, but for completions sake I will note a few things:

• While the possibility that it'll ever come up in a real world example and the behaviour isn't wanted is low: If you put Horizontal Expansion high enough that it merges spikes (creating holes) those holes will also be expanded.
• From a code-clarity perspective, it would'be been a bit more clear to put this where the other ('normal') horizontal expansion takes place.

[smartavionics]

Feel free to move the setting elsewhere if you wish.

[rburema]

Feel free to move the setting elsewhere if you wish.

I know, just a bit strapped for time right now :-)