switching to Popen to be python 2.6 friendly

tests/test_rst2ipynb.py

@@ -1,26 +1,28 b''
 import os
 import errno
 import os.path
 import subprocess
 import nose.tools as nt
 
 test_rst_fname = os.path.join('tests', 'tutorial.rst.ref')
 ref_ipynb_fname = os.path.join('tests', 'tutorial.ipynb.ref')
 test_generate_ipynb_fname = os.path.join('tests', 'tutorial.ipynb')
 
 
 def clean_dir():
     "Remove generated ipynb file created during conversion"
     try:
         os.unlink(test_generate_ipynb_fname)
     except OSError, e:
         if e.errno != errno.ENOENT:
             raise
 
 
 @nt.with_setup(clean_dir, clean_dir)
 def test_command_line():
     with open(ref_ipynb_fname, 'rb') as f:
         ref_output = f.read()
-    output = subprocess.check_output(['./rst2ipynb.py', test_rst_fname])
+    proc = subprocess.Popen(['./rst2ipynb.py', test_rst_fname],
+                            stdout=subprocess.PIPE)
+    output = proc.communicate()[0]
     nt.assert_equal(ref_output, output)