trailing whitespace

Suspend multicons output to the old console device while replaying
the vcons msgbuf.

add a cache so when we update the screen we only redraw the character cells
that actually changed since last time. This gives a noticeable speedup on
slower hardware with dumb framebuffers.
For now t

add a cache so when we update the screen we only redraw the character cells
that actually changed since last time. This gives a noticeable speedup on
slower hardware with dumb framebuffers.
For now this works with VCONS_DRAW_INTR and VCONS_DONT_READ only.

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add vcons_replay_msgbuf() for use by wsdisplay drivers to replay the message
buffer when attaching so older log messages will show up in the scrollback
buffer
Idea from gimpy