No Clobber sleeping

[machawk1]

From https://code.google.com/archive/p/warrick/issues/12

When the "no clobber" option is picked, and a file is detected to already exist, Warrick should not do any sleeping while moving on to the next file in the frontier. This will greatly enhance the usability of Warrick, and reduce the need for session management with the *.save files, and would be far more flexible. The most difficult part of the documentation to understand is the *.save feature used for saving sessions.