Cleanups and simplifications

My last PR added some lines, so this has removed some again :)

It
 - Fixes a minor merge error
 - Makes the naming behaviour of do_repository_work clearer
 - Makes it impossible to do_repository_work on the core module
 - Assorted cleanups

Number three on the list is probably worth emphasis - I can't see how this could have worked anyway (because we do it immediately after another do_repo_work, so we try and commit twice!?) and it seems entirely pointless because we just get an image tag of '0.0'.

(all untested)