Skip test_examples if IPython>=1.0 not available

Previously this would just fail. Now, we skip example testing if
IPython is not installed, or a version < 1.0 is installed.

Note that the additional monkey patching of
`_pytest.capture.DontReadFromInput` is due to a bug in how pytest
and IPython 0.12.1 interact. They both change sys.stdin, in
incompatible ways. Adding these two functions allows them to coexist
long enough for us to detect that an old version of IPython is
installed so we can skip the tests successfully.