Add optional 'sizehint' argument to readlines(). After approximately

Add optional 'sizehint' argument to readlines().  After approximately
this many bytes have been read, readlines stops.  Because of
buffering, the amount of bytes read is usually at least 8K more than
the hint.

Also changed read() and readline() to use PyArg_ParseTuple().

(Note that the *previous* checkin also fixed error handling and
narrowed the range of thread unblocking for all methods using
fread().)