Proposal : Power Venting

[ If we're using batteries, we should have some sort of cap on maximum power (which could be changed by buying extra cells, I suppose, later). ]

Add to end of the MCP:-

// Vent excess power.

if (power(self) > 100)

{

  power(self) = 100;

}

Also replace "power_unit" with "power", in the rest of the MCP, as that got missed when we renamed Power Units.

Enacted by est, 23rd Sept. +12 to Kevan, +5 to est