Fix checksum support to be compatible with Windows.

R=maruel@chromium.org
AUTHOR=cmp@chromium.org

Review URL: https://chromiumcodereview.appspot.com/9956052

git-svn-id: svn://svn.chromium.org/boto@4 4f2e627c-b00b-48dd-b1fb-2c643665b734
2 files changed