implement options TERMINAL_{KERN,NORM}_ATTR. These are aliased to
SC_{KERNEL_CONS,NORM}_ATTR and like these latter, allow to change the
default colors of normal and kernel text respectively.
Note on the naming: Although affecting the output of vt(4), technically
kern/subr_terminal.c is primarily concerned with changing default colors
so it would be inconsistent to term these options VT_{KERN,NORM}_ATTR.
Actually, if the architecture and abstraction of terminal+teken+vt would
be perfect, dev/vt/* wouldn't be touched by this commit at all.
Reviewed by: emaste
MFC after: 3 days
Sponsored by: Bally Wulff Games & Entertainment GmbH
vt_grow may be called with a new size that's larger than previous but
does not require reallocation - for example, when the number of columns
is the same and new number of rows is less than the history size.
Prior to this change we would fail to update vb_scr_size, and then hit
a KASSERT when trying to write to the newly visible rows.
Sponsored by: The FreeBSD Foundation
