Folks, I've made a few changes to locore.s (basically Chuq's patch posted
here earlier) that makes a newly selected process after a context switch
run at splclock() rather than splhigh().  This should solve all serial
line overflow problems and will probably allow operating any port
at 51200 baud.

The problem was (and has always been) the hefty context loading operation
in ctx_alloc() on sun4c MMUs (which was carefully placed outside the
splpmap/splx scope, so changing just the definition splpmap() did not
have any effect. splpmap can probably be omitted entirely from ctxalloc()
anyway).

-pk