When adding new functions to an extension you need to bump the version of the extension by renaming the file, updating the .control file, creating an upgrade script, and updating the Makefile to include the new files.
Attached is a new version of the patch, adding an upgrade script and the rest of it. Note that because, as Fabien noted, there's doesn't seem to be a way to add send/receive functions with ALTER TYPE, I did that by updating pg_type directly - hope that's OK.
