Fix unicode input in prompt mode in python2

shlex.split() in python2 doesn't work very well with Unicode as
proven already in #66, so we're using ushlex when running on python2.

topydo/cli/Prompt.py

@@ -24,9 +24,13 @@ from topydo.cli.CLIApplicationBase import CLIApplicationBase, error, usage
 from topydo.cli.TopydoCompleter import TopydoCompleter
 from prompt_toolkit.shortcuts import prompt
 from prompt_toolkit.history import InMemoryHistory
+from six import PY2
 
 from topydo.lib.Config import config, ConfigError
 
+if PY2:
+    import ushlex as shlex
+
 # First thing is to poke the configuration and check whether it's sane
 # The modules below may already read in configuration upon import, so
 # make sure to bail out if the configuration is invalid.