scripts for producing powheg precompiled tar ball

This script is used to create powheg precompiled tar ball. Compared to previous versions, we add error handling. If a working directory exists, the script moves the existing directory to old_${name} and LHE file to old_output.lhe. If the script fails to retrieve data card/tar ball or fails to compile pwhg_main, an error message is printed and the job exits and stops running.