FileNotFoundException messages are too non-specific

For example, the FileNotFoundException messages I see for "cat > foo" amd "cat > jnode/missing-dir/foo" are the same. In the former case, the exception is happening because (it seems) it is illegal to create files in the root of the namespace. In the latter case, the exception is happening because of the missing directory.

The exception messages need to specify the root cause of the failure. Without this, commands have no chance of producing helpful error messages for the end user.