There is only one s.PageTarget() - so we cannot change it, even tempoararily. We...

There is only one s.PageTarget() - so we cannot change it, even tempoararily. We have to find another solution to this.
...

Prevent 404.html from prettifying into 404/index.html

Restore @realchaseadams's commit 348e123
"Force `UglyUrls` option to force `404.html` file name"
which got lost after some refactoring (commit 8db3c0b).

Remove the equivalent "force `UglyUrls`" code for `sitemap.xml`
because the refactored code now calls `renderAndWriteXML()`
which uses `WriteDestFile()` which does not prettify a filename.

Fixes #939 (reverted from commit c4c19ad303cb11616a7291bdbeec997e59b6d24e)