I migrated to a new subversion server but one of the working copies was still pointing to the old one. I have checked in over one hundred revisions and I don't want to lose my check-ins. I am going to answer this myself, but I think others may find it useful.
[Below added on 2014 February 18]
To be clear, since I was downvoted by someone who left no feedback and the question below seems to not understand the situation.
I had three different working copies pointing to a repository. I migrated the repository to a new server. Unfortunately, I pointed two of the working copies (directories) to the new server, and accidentally left one pointing to the old repository. I continued to check in source code. By the time I realized that this working copy was checking code into the wrong repository, there were over 100 check-ins to the WRONG repository and about 300 to the new repository. Not so hard to merge, except that one of the files had been renamed. Somehow, I managed to rename the file in BOTH repositories, so it was NOT just a matter of dumping 100 transactions from old repository and loading them into new repository. Only one of the rename events could be present. I chose to bypass the rename in the new repository, since that was the only transaction that I could find which involved this directory or files in it. I hope this clarifies the mess that I caused, and why it was tricky to clean up.