This prevents multiple instances of FMSLogo from running on GNU/Linux unless to they were given a specific program to run.
The CreateMutex logic on Windows was preserved until it can be confirmed that wxSingleInstanceChecker can grab the exact same mutex.
Otherwise, FMSLogo 8.5.0 couldn't detect if FMSLogo 8.4.0, the installer, or the uninstaller is running, and vice versa.
