Added support for parallel checkpoints in backup_function.sh.
Added doc for parallel checkpoints in new Instance Vars template.
Formal docs to be added in a future release.
Upgraded Instance Vars template to v1.5, and updated sdp_upgrade.sh accordingly.
Fixed bug where PROXY_TARGET, PROXY_PORT, and PROXY_V_FLAGS were not
preserved across SDP upgrades.
Added notes about what can and cannot be changed in the
Instance Vars template for settings to survive future upgrades.
Added notes about sourcing the SDP environment in the instance vars file.