redirect-to-login-page: drop html-tags code (thanks to Thomas Hintz)

This fixes a bug introduced in 03e4e6b9ca2378928fa35c5b8b68738561010aa2

Thanks to Thomas Hintz for reporting that and suggesting removing
html-tags code.
use-sxml keyword param for define-page and ajax & friends take precedence over enable-sxml

use-sxml can now be used to disable SXML mode for certain pages and
ajax handlers when bound to #f.

Thanks to Thomas Hintz for reporting that issue.
`on' support for ajax & friends
Bump version to 0.39.2