Fix 3k's sphinx-build.py so that the version detection works with 2.x and 3.x.

Doc/tools/sphinx-build.py

@@ -12,12 +12,12 @@ import sys
 if __name__ == '__main__':
 
     if sys.version_info[:3] < (2, 4, 0):
-        print("""\
+        sys.stderr.write("""\
 Error: Sphinx needs to be executed with Python 2.4 or newer (not 3.0 though).
 (If you run this from the Makefile, you can set the PYTHON variable
 to the path of an alternative interpreter executable, e.g.,
 ``make html PYTHON=python2.5``).
-""", file=sys.stderr)
+""")
         sys.exit(1)
 
     from sphinx import main