Make sure importing ipdoctest does NOT start an ipython instance
Currently, ipdoctest has a special function called start_ipython() that starts an ipython instance globally. This is called unconditionally upon import of ipdoctest, and it is done this way because I was never able to debug exactly why if I tried to defer this call until later, the test suite had problems.
But ultimately this is a very nasty side effect, and indeed this global ipython was masking issues with other code because it would not show hidden dependencies on a running ipython.
For 0.10 we'll leave it as-is, but after the reorganization this needs to be cleaned up for 0.11.