* src/vte.c(vte_terminal_scroll_region): force an entire window repaint if
	we're supposed to scroll the background but we're not scrolling the
	entire window.  This means we need to repaint the scrolled region, and
	to keep things looking right, we need to repaint everything.
* src/vteapp.c(main): enable visible bell if we're disabling the audible bell,
	and vice-versa.
* src/vte.c: flesh out some doc comments.
* doc/reference/tmpl/vte.sgml: flesh out some notes on signals.