Apply anonymous SF patch #441229.

  Previously, f.read() and f.readlines() checked for
  errors on their file object and possibly raised an
  IOError, but f.readline() didn't. This patch makes
  f.readline() behave like the others.

Note that I've added a call to clearerr() since the other calls to
ferror() include that too.

I have no way to test this code. :-)

Objects/fileobject.c

@@ -847,6 +847,12 @@ get_line(PyFileObject *f, int n)
 		if (c == '\n')
 			break;
 		if (c == EOF) {
+			if (ferror(fp)) {
+				PyErr_SetFromErrno(PyExc_IOError);
+				clearerr(fp);
+				Py_DECREF(v);
+				return NULL;
+			}
 			clearerr(fp);
 			if (PyErr_CheckSignals()) {
 				Py_DECREF(v);