Increment version to 4.2.4.
Added --setup-only option to mod_wsgi express.
Fix one off error when checking limit on the number of supplementary groups for the daemon process group.
When there is any sort of error in setting up daemon process group, kill the process rather than risk running in an unexpected state.
Add release notes for 4.2.4.
Merge branch 'feature/daemon-startup-fixes' into develop