Suggested solution for rail placement issues

[mward]

TL;DR

Automatically switch to ghost build mode depending on distance. Use shift to force removal of obstacles in ghost build mode.

What ?

1. Clicking without shift:
   1. If the whole rail is within reach: direct build mode
   2. When any part of the rail gets out of reach, automatically switch to ghost build mode while avoiding obstacles"
2. Clicking with shift or pressing shift enters ghost build mode while removing obstacles. Releasing shift switches back to the other mode (avoiding obstacles either direct build or ghost build depending on the range)

If you really must place a short length of ghost which is within reach, and do not want to direct build it, then you simply have to move out of range first.

Why ?

This allows cliff avoiders to carry on avoiding cliffs, but also follows the player's natural instinct to press shift when they are ghost buiding and see an obstacle that they want the bots to remove.