API breaking change: email-blacklist and echo-notifications-blacklist
As part of work on T198935, the representation of preferences
`email-blacklist` and `echo-notifications-blacklist` returned by API
meta=userinfo has changed. Previously, they were by mistake returned as
arrays, which is unheard of in the API and resulted in weird output,
especially in XML:
At the same time, to change these preferences, you still had to use the
same format as DB storage, strings with newline-separated numbers. To
address this as well as a few other problems with conversion of preferences
on the storage-HtmlForm boundary, a fix has been implemented that turned
these preferences newline-separated strings everywhere.
This fix will be deployed to WMF production next week. According to our API
usage analysis, there are unlikely any users this might affect, however
still please make sure you're ready.