No clear error message when destination is a directory

[ggeldenhuis]

If you specify directory and not a specific file for the destination then the resource declaration for wget::fetch silently fails. My expectation was that it would save the file to a directory if I specify a directory and save it to a filename if I specify a filename. Also having an error message if that is not the expected behaviour would be great.

[Vincent--]

See c40bfa3
Not released yet, but if you use the last version from git, that should work ;-)