[couchup]: warn if [replicator] connection_timeout is low on dbs with lots of deletes

[janl]

Expected Behavior

Upgrading a database with many deleted docs using couchup just works™.

Current Behavior

When upgrading a database with lots of deleted docs, the default [replicator] connection_timeout of 3000 (which is translated to 10000 for _changes requests), won’t be enough to filter through all deleted docs with in 10 seconds.

The result is that replication first slows down and then stalls as _changes requests timeout messages show up in the logs.

Possible Solution

couchup could detect the low timeout and big deleted document count and suggest raising the config value (or even offer a way to do it from the cli right away), say couchup --raise-that-limit e.g.