[AC21.5] Support builtin functions in find-function (crash in C-h f)

APPROVE COMMIT 21.5 sjt> Adding 1 to the dimension of buf fixes the crash for me. sjt> Please review and make sure that's everything. Well, I'd still like review from Aidan, but since it fixes the crash for me and hasn't caused any other symptoms, may as well commit it. -- School of Systems and Information Engineering http://turnbull.sk.tsukuba.ac.jp University of Tsukuba Tennodai 1-1-1 Tsukuba 305-8573 JAPAN Ask not how you can "do" free software business; ask what your business can "do for" free software.