BSP tag importing does not recreate +seamsealer

[csauve]

This is applicable to H1 BSP importing, and presumably H2 if it has seamsealer. Both +seamsealer and +sky result in collision surfaces with collision material index -1. The toolset is currently assuming these faces are +sky on import, however it's possible to infer whether or not the surface was +seamsealer based on if the containing cluster is indoor (sky index -1), rather than outdoor. This is because exposure to seamsealer does not cause a cluster to be considered outdoor the way that +sky<n> do.

This is a non-trivial implementation because you'd need some code to lookup the cluster of that surface. There's no handy cluster index available.