Should not warn about shutting down kernels if not relevant

[hmeine]

When using the %qtconsole magic from an existing notebook (e.g., for %debug'ging), I get the "kernel will be shut down" warning when trying to close the window. Shouldn't it be possible to see in the code that the qtconsole does not "own" the kernel (or that the kernel usage count is >= 2, if it is refcounted) and to only show the warning if relevant?

[takluyver]

It should be, though it's a bit complicated because the Qt console can have multiple tabs connected to different kernels. That shouldn't be a showstopper, though.