(to_timespec): Change 1000000 multiplier to

(to_timespec): Change 1000000 multiplier to
1000000000.
(unchecked_unlock_sym, allow_external_unlock_sym,
recursive_sym): Use SCM_SYMBOL.
(scm_make_mutex_with_flags): When raising unsupported option
error, report what the unsupported option was.
(fat_mutex_unlock): When raising errors, unlock m->lock first.
(fat_cond_timedwait): Removed.
(scm_timed_wait_condition_variable): Call fat_mutex_unlock
directly instead of via fat_cond_timedwait.