formatter: port handling of 'originalnode' to populatemap() hook This isn't a pure templating business, so let's move out of the templater module. Note that this works only in web templates where mapping['node'] is a static value.

templater: switch 'revcache' based on new mapping items It was pretty easy to leave a stale 'revcache' when switching 'ctx'. Let's make it be automatically replaced.