Wipe old job files

Remove the job files once they're done with.  Once they're in Amber you don't need them anymore.
upgrade to 1.1.73 of AmberDB
ignore emacs things.
Clear out the working directory

Clear it by removing all the files in the job's working dir.  Throw exception if any of those files is a directory (which should never happen!).
Merge pull request #345 from nla/hr-wipejobfiles

Wipe old job files
Merge remote-tracking branch 'origin/master' into hr-cmstrs

* origin/master:
  Clear out the working directory
  ignore emacs things.
  upgrade to 1.1.73 of AmberDB
  Wipe old job files