Disjunctions on time ranges should result in error instead of treating as conjunction

A query like:
```
select mean(usage_user)  from cpu where hostname = 'host_99' and time > 1 or time <= 1;
```

is treated the same as if the 'or' were an 'and'. This means it returns no results whereas it should return all rows. If disjunctions on time aren't meant to be supported, an error should be returned instead of an empty result set.