allow --help and config_file classes to differ

override help_classes or config_classes
to allow them to differ from App.classes
only include kernel config in `--help` output

don't write it to a config file that won't be read
ipython_kernel gets its own config file
skip test_not_writable_ipdir if I can't create a non-writable dir

such as when running as root

just came across this running iptest in a docker container. This was the only test that failed.
on_atomic_change -> on_some_change
Merge pull request #6549 from SylvainCorlay/some_update

on_atomic_change -> on_some_change
run iptest in Dockerfile

and install sphinx with apt, since it's super slow
because of 2to3
Use some more informative asserts in inprocess kernel tests

Prompted by gh-6552 (but doesn't fix it)
Merge pull request #6546 from minrk/root-no-write

run iptest in Dockerfile
Merge pull request #6556 from takluyver/inproc-kernel-tests-better-assets

Use some more informative asserts in inprocess kernel tests
added import command

I added the command to import `IPython.parallel` and imported `Client` from it to be consistent with this page:

http://ipython.org/ipython-doc/dev/parallel/parallel_multiengine.html#creating-a-directview-instance
Merge pull request #6550 from drevicko/update-parallel-magic-doc

Update parallel magic doc
Added missing quote in iframe height property.
Merge pull request #6564 from rossant/iframe-height-quote-missing

Added missing quotation mark in iframe height property
Fixes #6561 instructions for installing dependencies on zsh/tcsh
Don't catch repr-errors in pretty

allow exceptions to be raised and displayed by the caller
show tracebacks for errors in formatters

instead of FormatterWarnings
handle missing 'text/plain' in displayhook

avoids KeyError when repr fails
Merge pull request #6569 from gcporras/fix_instructions_for_installing_project_dependencies

Fixes #6561 instructions for installing dependencies on zsh/tcsh
Merge pull request #6394 from minrk/repr-fail-traceback

show traceback for broken reprs