add pickleutil.PICKLE_PROTOCOL

instead of hardcoding `-1`.

default to DEFAULT_PROTOCOL if defined (Python 3.4), and HIGHEST_PROTOCOL otherwise.

Matches dill behavior
add IPython.utils.log.get_logger

simple utility for getting the global logger

- from the Application instance, if running
- Python root logger, if not
use utils.log.get_logger where appropriate
fix stream output created by raw_input

was using incorrect 'name', when it should have been 'stream',
creating invalid content in notebook documents.
fix a couple of invalid notebooks

found via validation in #6045
Merge pull request #6047 from minrk/invalid-notebooks

fix a couple of invalid notebooks
Merge pull request #6044 from minrk/core.log

add IPython.utils.log.get_logger
Merge pull request #6046 from minrk/raw-input-invalid

fix stream output created by raw_input
Merge pull request #6029 from minrk/dumps-protocol

add pickleutil.PICKLE_PROTOCOL