Prevent ipython.py launcher from being imported.

ipython.py

@@ -1,18 +1,23 b''
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 """IPython -- An enhanced Interactive Python
 
 The actual ipython script to be installed with 'python setup.py install' is
 in './scripts' directory. This file is here (ipython source root directory)
 to facilitate non-root 'zero-installation' (just copy the source tree
 somewhere and run ipython.py) and development. """
 
+if __name__ != "__main__":
+    raise RuntimeError('You are trying to import the ipython.py executable. '
+            'Did you mean to call "import IPython" (case-sensitive) instead?')
+
 # Ensure that the imported IPython is the local one, not a system-wide one
 import os, sys
 this_dir = os.path.dirname(sys.argv[0])
 sys.path.insert(0, this_dir)
 
 # Now proceed with execution
 execfile(os.path.join(
     this_dir, 'IPython', 'scripts', 'ipython'
 ))
+