Incorrect parsing when executing %debug print('m n')

II ran into this issue with a more complicated command and distilled it to this testcase. Other print commands, for example `%debug print('mn')` without the space can be debugged. Also, any other function instead of `print` yields the same result:

```
$ sage -ipython
Python 2.7.8 (default, Feb 15 2015, 03:39:19)
Type "copyright", "credits" or "license" for more information.

IPython 3.0.0 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.

In [1]: %debug print('m n')
NOTE: Enter 'c' at the ipdb> prompt to continue execution.
---------------------------------------------------------------------------
SyntaxError Traceback (most recent call last)
SyntaxError: EOL while scanning string literal (, line 1)
```