Errors building addins in 8.1.15 with `pack_rebuild`

[ninjarobot]

@JanWielemaker did something change with how addins are installed between 8.1.12 and 8.1.15? With 8.1.15, we are getting this error building addins with pack_rebuild:

ERROR: -g pack_rebuild(space): pack `space' does not exist

docker-library/official-images#6821 (comment)

[JanWielemaker]

Thanks for looking into this. Yes. The location where packs are installed has changed. Actually the changes in 8.1.15 are still immature, so I propose to skip this for Docker and (soon) build 8.1.16.

[JanWielemaker]

I've released 8.1.16 and created a pull request. In addition to the necessary changes, this also include library(yaml). Please review and publish if you agree.

[ninjarobot]

Fixed by a2509b4