sql: Clarify comments on query()/query_next() return values
sql: Clarify comments on query()/query_next() return values

- Clarify that the return values of query() and query_next() are exactly
equivalent to (query_ok() || query_has_row())

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr