Clairvoyance performance

[cooljeanius]

This might be an upstream Wesnoth issue, but I'm wondering if there's any way to improve the gamespeed performance when using Yumi's "clairvoyance" ability? Maybe instead of considering all tiles next to allied units as valid teleport targets, just consider the tiles occupied by allied units as the teleport targets instead, and then let the game handle the part where the code preventing multiple units from occupying the same tile shunt her to an adjacent tile? I'm thinking reducing the number of valid teleport targets might reduce the amount of pathfinding code that the game has to handle...