Support for CockroachDB (pull req available)

[muxator]

Hi,

I have opened a pull request on ueberDB (ether/ueberDB#99) for supporting native UPSERTS on the PostgreSQL driver.

This gives better performance for PostgreSQL >= 9.5, and makes Etherpad compatible with this distributed database.

Tested on PostgreSQL 9.4, PostgreSQL 9.5, and CockroachDB.

[muxator]

I guess the CockroachDB is never going to be added unless (ether/ueberDB#99) is merged, which at this point seems unlikely.

Thank you, anyway.