Latest GUI stuff and no more 'dynamic'

These were fixes for #93, but they unfortunately don't catch the case of misspelt paths in the CKAN metadata, because we generate the file lists well before we start copying around zip entries. So I'm reverting this change (because an exception from CopyZipEntry *is* exceptional, we only ask it for things which we know are in the zipfile), although I'm not reverting all of the commit it came from because it seems to be tangled with other changes.