Feature/allow-exiting-watch-return-code

[jeanbaptistelab]

Add a new "-e" command line option to specify that the watch command should exit when the command returns the given status

[troelsjessen]

I doubt CSH users are aware of integer values of return codes.
How will it work out if we break on all failure return codes?
Perhaps we can divide the error codes into groups, so user can specify that he wants to break on communication-related errors etc?