Thanks for looking at this. It will be next week before I can test any changes and put up a new, tested diff. I'm away from home at the moment and don't trust doing a restart remotely. I've managed to get the restart working more often that not (it simply doesn't work by default) but haven't got anything working well enough to publish or trust

That attribution is fine

Change now includes update allowing creation of xbootldr partition type with gpart (without specifying uuid).
System with change boots normally (the actual table is in the kernel, not the gpart utility).
Gpart utility now creates and reports on xbootldr partition type as well as existing types (about 20 tested on a memory disk).

Definition of XBOOTLDR partition type moved to gpt.h
Changes to gpart utility suggested still being tested so not shown

Changes pretty much as suggested by mhorne. More concise code and no messages.