Low interest rates, growing consumer confidence and warm summer weather are combining to buttress Douglas County's housing market.Residential sales continue to climb in the county, according to figures released this week by Portland-based RMLS.Last month, 88 listings closed, bettering May 2001's mark by seven houses -- an 8.6 percent increase.The increase follows a dramatic April, when sales leapt 60 percent, from 109 home listings closed this year compared to 68 in April 2001. April also registered a big jump in pending sales -- 130 compared to 96 in April last year, a 35 percent increase.Year to date, closed residential sales …