Floatlands terrain discontinuous over chunk boundaries, due to noise index in xzy loop.

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New comments on original pull here #555
The floatland mapgen code is here https://github.com/minetest/minetest/blob/master/src/mapgen_indev.cpp#L347
More details in IRC logs http://irc.minetest.ru/minetest/2013-11-08#i_3421936 05:19 to 05:40.
From that, suggested solution by hmmmm:
05:38 hmmmm so what I'd suggest is changing the loop order to z, y, x, keeping the increment on the 3d noise index
05:39 hmmmm then for the 2d noise, calculating it by z * scanline_size + x
05:40 hmmmm zstride = node_max.X - node_min.X + 1;
05:40 so int index2d = z * zstride + x

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In the current code and in my flolands mod version 0.2.1, the [x[z[y]]] loop works column by column, so 'float noise3' and 'float pmidy' only need be to calculated once per column.
In the suggested solution above, the [z[y[x]]] loop means that 'float noise3' and 'float pmidy' need to be calculated once per node, so they need to be moved inside the inner x loop.

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Here's my attempt at the fixed mapgen code https://forum.minetest.net/viewtopic.php?pid=117500#p117500

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That code was tested by us^0gb and seems to work, see IRC logs from 06:14 here http://irc.minetest.ru/minetest/2013-11-09#i_3423875

[proller]

0gb-us: please fix spaces->tabs in patch