update posts set post_content=replace(post_content, '<a href="http://fixpoint.welshcomputing.com', '<a href="http://jfxpt.com');
update comments set comment_content=replace(comment_content, '<a href="http://fixpoint.welshcomputing.com', '<a href="http://jfxpt.com');

and a couple hand-edits for the occasional peculiar reference turned up by

$ mysql fixpoint -re "select replace(post_content, '<', '\n<') from posts" | grep '^<a' | grep fixpoint.welshcomputing | sort