Be lenient when rebuilding cases

From what I can tell, this is the main cause of http://manage.dimagi.com/default.asp?123037. I'm also adding logging in there so I can get more information about _why_ it happens, so I can fix any more underlying cause.
Yeah it's true. One of the first steps in the function is to strip out all creates if lenient or just the first one if it's strict (so that it can fail hard later when it tries to apply a create). See: https://github.com/dimagi/casexml/blob/rebuild-no-strict/casexml/apps/case/models.py#L964.