Support redirecting to absolute URL from this.redirect in preload

[antony]

As discussed in the Sapper discord.

In a preload method inside a page, you can call this.redirect to redirect the page before it renders.

this.redirect(301, 'some/url')

It would be advantageous (for instance, in the case of adding SEO mappings for legacy urls), if we could redirect to external urls (i.e. another website).

One possible way of doing this would be:

this.redirect(301, 'https://www.some.other/url', true)

where the third parameter defines whether the url is absolute (true) or relative (false).

[Rich-Harris]

Fixed in 0.24!