Fix .tar.gz unpacking in Windows

From http://docs.python.org/2/library/os.html#os.open:

"In particular, on Windows adding O_BINARY is needed to open files in binary mode"
Fix invalid open() flag on non-Windows machines

O_BINARY seems to be Windows specific.
Merge pull request #55 from bogdanm/fix-win-unpacking

Fix .tar.gz unpacking in Windows