Fix cygtar on win32 so it doesn't make archives containing  world writable files.
Fix cygtar on win32 so it doesn't make archives containing 
world writable files.

For some reason os.stat() always sets the world writable
flag and python's tarfile was taking this as the default
mode in the archive.

BUG=153018

Review URL: https://chromiumcodereview.appspot.com/11199005

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@10055 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client