Simplify solock() and sounlock(). There is no reason to return a value

Simplify solock() and sounlock(). There is no reason to return a value
for the lock operation and to pass a value to the unlock operation.
sofree() still needs an extra flag to know if sounlock() should be called
or not. But sofree() is called less often and mostly without keeping the lock.
OK mpi@ mvs@