Implement setuid/setgid when spawning child processes
Implement setuid/setgid when spawning child processes

* New "uid" and "gid" fields in task structures.
* Adds options -u/-U/-g/-G for setting user/group credentials, both for main
  command and logging command.
* Master process does not drop privileges. Doing that would make impossible
  for it to respawn child processes with the desired credentials.

aperezdc/dmon