Fix a dex format buffer by setting all checksums

          :rtype: string

def fix_checksums(self, buff):
        """
          Fix a dex format buffer by setting all checksums

          :rtype: string
      """
        import zlib
        import hashlib

        signature = hashlib.sha1(buff[32:]).digest()

        buff = buff[:12] + signature + buff[32:]
        checksum = zlib.adler32(buff[12:])
        buff = buff[:8] + pack("=i", checksum) + buff[12:]

        debug("NEW SIGNATURE %s" % repr(signature))
        debug("NEW CHECKSUM %x" % checksum)

        return buff