Error report to the user

[Rafiot]

We need to have a way to inform the user when something goes wrong.

Examples:

• The destination key run out of space
• The source key is empty
• /tmp was full
• unable to read the key (src or dest)
• file system unsupported
• key not there
• permission problem
• what happened on a file if it did not work
• file broken
• archive bomb

Very important: the log files have to be usable (*.log files, is it enough ?)

Please add the errors you would to see reported