Don't pass IPython-specific args to non-IPython kernels

add a few FIXME notes that the IPython-kernel special treatment
will probably want to be removed in the Jupyter explosion.
update MappingKernelManager module docstring
Merge pull request #6961 from minrk/profile-dir-no-3p

Don't pass IPython-specific args to non-IPython kernels
Merge remote-tracking branch 'upstream/master'