svn: Commit failed (details follow): svn: Server sent unexpected return value (405 Method Not Allowed) in response to MKCOL request for '....'
ServerFault had the answer. Google code allows anonymous checkout with HTTP, but commits require HTTPS. So, I exported my local workspace changes, blew away the workspace, checked out again with HTTPS, and imported my changes. No commit problems after that, and thank goodness once again for the amount of readily-available information on the Internet.