Always try to load icons as PNG format.
Always try to load icons as PNG format.

This reduces the risk from buggy image loaders, since only flaws in the
PNG loader will now affect us.

git-svn-id: eb86470c0dbc9d881c76e652f76111a30a15f3d1@740 9f8c893c-44ee-0310-b757-c8ca8341c71e

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