Formatting output numbers with digit separators

This change makes large output numbers more readable. Most of them are in the order of 1,000,000,000
returning the size of filtered data
waiting of asynchronous kernel calls to measure elapsed time correctly.
bug fix in compute prefix sum
Actually filtering data in GpuFilteredRDD after filling it with data
formatting and cosmetics
Adding a testcase for compute
Adding a test case for GpuFilteredRDD
cosmstics
Fixing bugs in test cases
commit to go home