Support for Mineshafts

[Paril]

Adds support for a Mineshaft layer to the map viewer.

[crbednarz]

Has this been tested for accuracy, and do you know what versions of Minecraft it would apply to?

[Paril]

Only tested on 1.7.10 - accurate on that version. Haven't looked back to see if it fit any other versions. Sorry for it not being more specific. I made this simply because I needed to find a Mineshaft in my world and this was quicker than scouring the world, heh.

[Paril]

I should mention I do know that this won't work in early 1.7/1.6 versions, as they had a different value in the RNG area (they had 0.1 instead of 0.02 or something like that). At the moment I am 100% sure it works with 1.7.10 but I can't really guarantee any earlier ones (1.7.9 is probably consistent. Basically until the last world gen change I would imagine).

[Treer]

Actually your layer works successfully all the way back to version 1.4.2.

Mineshafts don't appear where predicted in v1.3.2 or earlier, so 1.4.2 is the version where this layer becomes accurate.

[Treer]

c7f971f3f70955b2543a6f9ca8cd0abf78068da0 makes this Mineshaft layer show the extra mineshafts present in versions prior to 1.7.2.

(my testing back to 1.4.2 confirmed all the mineshafts in the layer were present, but because v1.6 has all the 1.7 mineshafts and more, my testing didn't expose the ones that were lacking. This change should fix that aspect)

And 9ebb54d4b0e33d7564ce9f377c969b1c51a90eae makes this Mineshaft layer compatible with all the versions that predate 1.4.2