There is a possibility of making the old master standby if you have promoted standby after clean-shutting down the master. I I tested this in 9.2.x and later versions. This is a manual process in 9.2, i think it is the same in 9.1.x version as well.
The process is -
- Ensure master and standby are in sync before switching over
- Promote standby
- build recovery.conf at old master with the parameter recovery_target_timeline set to 'latest'
- When you start the old master, it will ask for timeline history files which you need to manually transfer from new master