Assume that score_open() and score_clear() always succeed.
Since the score table has only volatile columns, the only possible
error is memory exhaustion, in which case we can only abort
anyway. This patch changes score_open() to abort if osl_open()
fails. This allows us to let score_clear() return void. We can't get
rid of the return value of score_open(), however, since a pointer to
this function is stored the afs table operations structure.