Attached is a patch to complete libCSS' widows and orphans property support.
I've also made small modifications to a few of the other internal 'page'
property setters (set_page_break_before) etc. to not set up a page struct if there's
not one already and the property's being set to its default value. Especially with
non-inherited properties, this seems to save a surprising amount of runtime when using
libCSS heavily (informal testing, paginating an ebook), and presumably a fair bit of RAM
too, especially as the page struct grows in size.