generator: Don't die if an API call isn't listed in API versions file. For example, it may just have been added.
docs: Which API calls were first supported in which upstream versions. Run src/api-support/update-from-tarballs.sh (this won't work unless you have a local copy of the tarballs from the website). src/api-support/added contains the result of running the script, a list of pairs: (API name, version first appeared).