On our RHEL5 systems we're getting 2 and sometimes 3 or more salt-minions started. Somehow the check on /var/run/salt-minion.pid doesn't prevent this.
This patch stops the registered process and kills any further salt-minion processes, first trying -TERM and then -KILL signals.
It may be that other distros would like to use this same logic to tidy up, in which case the new code can be moved into place as appropriate.
This also fixes an issue with sourcing of /etc/rc.d/init.d/functions in
RHEL/CentOS/Fedora/etc., allowing the use of /etc/default/salt to
override environment variables.
With this commit it is possible to use virtualenv with the init scripts.
For example, I have this in my /etc/default/salt:
```
SALTMASTER=/srv/venvs/venv-1/bin/salt-master
SALTMINION=/srv/venvs/venv-1/bin/salt-minion
SALTSYNDIC=/srv/venvs/venv-1/bin/salt-syndic
SALTAPI=/srv/venvs/venv-1/bin/salt-api
PYTHON=/srv/venvs/venv-1/bin/python
```