Fixing systemd service so PMS can't startup on top of it self.

Built in check when enabling and disabling to ensure upgrading from old to new rpm stops the old named service.
Added check for stopping PMS on upgrade.

Added checks for systemd when stopping PMS on upgrades.
Merge remote branch 'upstream/master'
Merge pull request #59 from ziggimon/master

Fix for Fedora 18, so we don't have PMS starting twice.