* lily/simple-spacer.cc (get_line_forces): test for non-fitting

	* lily/simple-spacer.cc (get_line_forces): test for non-fitting
	line even if we precede a forced break.

	* lily/optimal-page-breaking.cc (try_page_spacing): square line
	forces too. Make page-spacing weight default to 10 because the
	changes to vertical springs decreased the page force/line force
	proportions. Also, take the average of line force and page force
	instead of just the sum.

	* lily/constrained-breaking.cc (initialize): make the stiffness
	of the vertical springs depend on the height of the system. This
	prevents pages with only a few large systems from getting huge
	forces

	* Documentation/user/page.itely (Page formatting): document the
	change in default page-spacing-weight

	* lily/include/constrained-breaking.hh: initialise bottom_padding_