dev/core#2073 Fix a real live leak

dev/core#2073 Fix a real live leak

I used the same methods I had been playing with on the test class on a contribution
import script and found that the object that was increasing in memory in tandem with
me increasing iterations was an instance of DB_result

I tracked it down to here. In essence our main DAO functions clean up after themselves - e.g
when the DAO is destructed it cleans up the globals it has created.

However, this older ->query() function does not do that and each time is is called increases it's memory hold.

It's also worth better caching in this function...