[RFC] Update code style to not indent case headers inside switches.

I thought this was the agreed style, but i can't seem to find the discussion….

With this change switch statements look like:

    switch (i) {
    case 0:
    case 1:
        return true;
    case 2:
        return false;
    default:
        return false;
    }

The reason i'd like this to be the style, is that this way a switch statement can be converted to/from an if/else block without changing the indent.

I'm thinking of restyling the entirety of mapgen.cpp, so as to be able to easily resolve conflicts in map_draw(), and also just to be able to read map_draw() without going insane.