From Gerri:

- Use basic tracing (i.e. w/o mutex locking) in the child  after forking
  and before execv; this is to avoid problems with locks during fork.
- fix a problem with the default image definition in reading a
 'worker/slave' line from the config file when a user name is
  defined (i.e. worker user@wrkhost).


git-svn-id: http://root.cern.ch/svn/root/trunk@18636 27541ba8-7e3a-0410-8455-c3a389f83636