Also switches scribble search trampoline to standard DOCTYPE.
Scribble's HTML output currently relies on the quirks-mode
box model for layout of the many tables used in rendering.
However, Scribble doesn't need the rest of the changes in
browser quirks modes, so we choose a DOCTYPE that just
changes the box model.
It's non-obvious how to replicated this formatting with CSS
in standard-mode rendering. Probably a better long term
solution is to move away from table-based layout.
See further discussion on GitHub pull request 158 here:
https://github.com/plt/racket/pull/158
