Iglus are not getting loaded

When i load my spigot world, im getting the following warning about 20 times:
`2016/08/22 08:43:02 [SEVERE] Unknown structure piece type to load: "Iglu"`

Using Glowstone `#220` from CI Server.

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Start by searching the Glowstone source for the warning text and the structure-piece loading path, using the reported "Iglu" type as the entry point. Compare how structure pieces are registered and loaded, then verify that the warning no longer occurs and iglus load when testing the affected Spigot world.

Written by the indexing model from the issue text.