Minor changes to the startup and shutdown code

Minor changes to the startup and shutdown code

- Update comments
- Close logs in LogManager destructor instead of relying on other code to do it
- Change return type of InspIRCd::Run() to void
- private: InspIRCd::CheckRoot()
- Change log message type of setgroups() etc. errors to "STARTUP"
- Load cmd_privmsg in PURE_STATIC builds