[[!template id=gitbranch branch=GiuseppeBilotta/scanif author="Giuseppe Bilotta"]]

When a directive that should be run during scan preprocessing is inside
an if directive, it doesn't get called because the if preprocessing does
not run during scan.

I've written a simple [[patch]] to fix the issue, currently hosted on the
scanif branch of my repository. The patch also passes the preview option
back to the Ikiwiki::preprocess call, making sure that whatever is being
reprocessed is done so in the same conditions as the original call.