Fix Windows unit tests

Author: tleonhardt

cmd2.py

@@ -34,7 +34,6 @@
 import os
 import platform
 import re
-import readline
 import shlex
 import six
 import subprocess
@@ -80,6 +79,13 @@
 except ImportError:
     ipython_available = False
 
+# Try to import readline, but allow failure for convenience in Windows unit testing
+# Note: If this actually fails, you should install readline on Linux or Mac or pyreadline on Windows
+try:
+    import readline
+except ImportError:
+    pass
+
 __version__ = '0.7.1a'
 
 # Pyparsing enablePackrat() can greatly speed up parsing, but problems have been seen in Python 3 in the past