Fix browser harness windows

Various fixes to running browser harness on Windows. Fixes the tests

browser.test_compression
browser.test_split_in_source_filename
browser.test_sdl_image_compressed
browser.test_freealut
browser.test_chunked_synchronous_xhr
browser.test_s3tc_crunch
browser.test_s3tc_crunch_split
and all tests that rely on the reftest.js mechanism to compare images.