Our code hardcoded "rcstart" in both string value and C++ class member name. This change is really a breaking one to us.
Could you tell me when this is released to *wiki?
The change is coming with 1.21wmf12. Due to a major bug in that release, I don't know when it will be deployed anywhere besides test2wiki.
Note that the "rcstart" parameter is not going away. It's just that the query-continue will start using "rccontinue" as a key rather than "rcstart". For the moment, you can compare [1] and [2] to see the difference.