Execute embedded scripts on overlay-page load.

Execute embedded scripts on overlay-page load.

* site.js (no_break, update_page_content_header): Delete them.
(set_page): New page-load helper function; it supports page title and
subtitle updates, when called from embedded scripts on overlay-pages.
(load_page) [status == 200]: Scan for, and execute embedded scripts.

* index.html [masthead] (h1, h2): Change identifiers from...
(as-page-title, as-page-subtitle): ...these respectively, to...
(page-title, page-subtitle): ...these; add hidden placeholder content.

* about.html contact.html fdl.html mailing.html missing.html
* terms.html [masthead] (dl): Delete hidden element; replace it with
script, to assign effective HTML content to each of...
(page-title, page-subtitle): ...these.

* fdl.html mailing.html (ol, ul): Do not override CSS styles.

* site.css [masthead]: Do not assume that final element is...
(dl): ...this; define style for immediately following paragraph, on
the basis that the final masthead element may be anything.