GLI does not show hidden files, but processes them when building

[mcennis]

When adding directories in the GLI, hidden files are not visible but are added and are processed during building. When these hidden files are valid files with known extensions, then they can create spurious entries in the collection and/or error messages/unprocessed file statements linked to no visible file.

[kjdon]

Preferences setting for "show all files" Also, ImagePLug could block Thumbs.db files