improve multiple results support

The specification talks exactly about -1:
> Returns: the current result as an update count;
> -1 if the current result is a ResultSet object or there are no more results

Other negative numbers can theoretically mean something different than „no more results“
e.g. unknown number of updates (?).

 # This code depends on make tool being used

 DEPFILES=$(wildcard $(addsuffix .d, ${OBJECTFILES} ${TESTOBJECTFILES}))

 ifneq (${DEPFILES},)

 include ${DEPFILES}

 endif