* src/ring.c, src/ring.h: add _vte_ring_insert_preserve(), which scrolls lost
	items off the top instead of the bottom, as _vte_ring_insert() does.
* src/slowcat.c (catfile): check that we didn't read an EOF before attempting
	to write it.  Skip the more complicated checks and just check that the
	file pointer isn't stdin before closing it.
* src/ssfe.c: cleanups.
* src/vte.c(vte_sequence_handler_sf): add lines to the scrollback area when
	scrolling is restricted but the top line of the area is the topmost
	visible line (Red Hat #75900).