Fixing Shell and python2 call

The recently added bpython support broke the IPython Shell because of methods with the same name as magic_method definitions added globally.

This also fixes the examples not running on systems having a python 2 and 3 installation.
For instance, in my case I incoked all SimpleCV scripts with 
<pre>python2 name.py</pre>
where as the default call for
<pre>example xx # ( in shell ) </pre>
invoked Python 3 and failed to execute.