Log missing assets on "fcache assets" found.  This ignores references found by scanning LSL/notecard files since these are the source of false positives.

This also changes UuidGatherer to reutn an AssetType.Unknown for embedded script/lsl references instead of Texture, since these are often not textures.
This is added to help people in determining when they have missing assets such as textures, etc.
In this case, one wants to run "fcache clear" first.