[mb4nck]

You can get pg_rewind for 9.4 (and 9.3 in its branch) here:

https://github.com/vmware/pg_rewind/tree/REL9_4_STABLE

It's from the people who wrote it upstream, they provide the code there for earlier Postgres releases.

[scurvy]

Does this help at all with upgrades? Upgrading from 9.4 to 9.5 means you need to rebuild your entire replication topology because the master's identifier has changed (in the initdb step of the official docs).