(1) Don't attempt aquire the non-recursive lock sio_lock recursively.
Doing so caused unbounded recursion in some setups. E.g., if DDB,
BREAK_TO_DEBUGGER and WITNESS are configured; if the debugger is
entered using a break, then WITNESS will actually detect the invalid
recursion and will add to it attempting to print a message about it.
(2) Don't use sio_lock before it has been initialized. The old check
(sio_inited != 0) didn't work when sio_inited was boolean because
sio_inited was set too early, and became just wrong when sio_inited
was changed to a tri-state variable in rev.1.348.
Reported and fixed in another way by: fenner (1)
b0e8a2af1f