Change unittest to default to 1 iteration of each test.  Can be change manually to 1000 for benchmarking purposes.
BUG=77
TEST=build\release\libyuv_unittest.exe
Review URL: https://webrtc-codereview.appspot.com/768006

git-svn-id: http://libyuv.googlecode.com/svn/trunk@336 16f28f9a-4ce2-e073-06de-1de4eb20be90