Offer more explicit errors than "permission denied"

[jay0lee]

Today if GAM can't open or write to a file it returns an error like:

ERROR: File: <path>  [Errno 13] : Permission denied <path>

that's not an awful error but we might be able to offer a bit more detail like:

ERROR: GAM cannot write to file <path>. Please ensure your user has permissions to write to this file on your filesystem.

or similar.