Code review comment for lp:~therp-nl/ocb-addons/lp754339

This branch is a (nearly) verbatim copy of the old trunk branch
https://code.launchpad.net/~therp-nl/openobject-addons/ronald@therp.nl_fix_invoice_pricelist_lp754339/+merge/142021

Ronald: Any chance you remember why you introduced the changes you mention?

The test sounds like a very good idea, setting to work in progress.