Make capsys more like stdio streams in python3. Resolves #1407.

_pytest/capture.py

@@ -12,8 +12,8 @@ from tempfile import TemporaryFile
 
 import py
 import pytest
+from _pytest.compat import CaptureIO
 
-from py.io import TextIO
 unicode = py.builtin.text
 
 patchsysdict = {0: 'stdin', 1: 'stdout', 2: 'stderr'}
@@ -403,7 +403,7 @@ class SysCapture(object):
             if name == "stdin":
                 tmpfile = DontReadFromInput()
             else:
-                tmpfile = TextIO()
+                tmpfile = CaptureIO()
         self.tmpfile = tmpfile
 
     def start(self):