p4master_run: Preserve original arguments list and use this when exec'ing as $OSUSER.
backup_functions.sh: Add text about sourcing p4_vars yourself instead of using p4master_run.
update_limites.py: Run p4login directly without p4master_run since p4login calls p4_vars now.
everything else: Remove comment block about needing to run with p4master_run. Reword comment
about SDP_INSTANCE since it is not always an integer value.