The `all` filter operator has shortcuts to optimise common patterns like
`[all[shadows+tiddlers]]` or `[all[tiddlers]]`. In those cases, the
filter operator function returns early and never uses the `result`
linked list that was created, so it's immediately garbage-collected.
Let's delay creating it until we know it's actually going to be used.
By rearranging the `[all[]]` operator we are able to ensure that shadow
tiddlers get processed before ordinary tiddlers. This makes it easier
to create custom stylesheets that override the core.
