Assume binary data when checking whether process's output is available.

[yuttie]

The hReady function takes account of the encoding of a given handle, and it checks whether one or more characters are available. Thus, it may fail with a decoding error.

I made the createp switch the mode of the handle cout to binary.

Since reading/writing functions from the Data.ByteString module originally don't care the encoding, this change only affects hReady.

[yuttie]

Any comments?