Skip plotting doctest and avoid deprecation warning.

Skip the plotting doctest in sympy/geometry/ellipse.py This fixes issue 3925: Failing doctest in sympy/geometry/ellipse
http://code.google.com/p/sympy/issues/detail?id=3925

Also change the ipython printing test to use init_printing(). This removes the following deprecation warning while running the tests:
```
sympy/interactive/tests/test_ipythonprinting.py[1] sympy/utilities/exceptions.py:149:
SymPyDeprecationWarning:

using %load_ext sympy.interactive.ipythonprinting has been deprecated
since SymPy 0.7.3. Use from sympy import init_printing ;
init_printing() instead. See
http://code.google.com/p/sympy/issues/detail?id=3914 for more info.

  warning(see_above, SymPyDeprecationWarning)
.                                                            [OK]
```