Adds p.break_ for explicit newlines in lib.pretty

p.break_() explicitly includes a newline while pretty printing, and maintains indentation.
A simple test is included to show this working.
Uses p.break_() when repr() is used for printing

When a newline is found in the result of repr() (using the default printer), the newline is replaced with an appropriate call to p.break_()
Use default OS shell to run system commands

Instead of using os.system which uses /bin/sh, this uses subprocess.call (the replacement of os.system) to run the command using the default shell of the OS. With this, one can use more advanced commands for bash, zsh, ksh, ...

I do not have a win32 system to test this modification, so maybe line 2236 can also be changed like 2239.
trigger `Kernel.status_started` after websockets open

This leads to a more logical state for event watchers to expect.
change default behavior of database task storage

The previous default behavior was to create a new table (sqlite) / database (mongodb) for each Hub instance,
so that task history would not be shared by subsequent IPython sessions.

I don't think this was the right choice,
so this PR switches the default behavior to use the table / database `ipython-tasks`.
The result is that all Hub sessions in a given profile will share history by default,
which makes the benefit of the db backends clearer.

Configurable behavior remains the same, only the default is changed.
quote table name

avoids syntax errors from hyphens
Added new option in %%cython cell magic to specify the module's name.
Add --name option in %%cython cell magic to specify the Cython module's name.
Use default OS shell to run system commands

Instead of using os.system which uses /bin/sh, this uses subprocess.call (the replacement of os.system) to run the command using the default shell of the OS. With this, one can use more advanced commands for bash, zsh, ksh, ...

I also edited the docstring, added comments and fixed the handling of return codes.
remove special handling of speaker notes
clarify `reveal-prefix` alias name
update nbconvert docs about reveal.js
add proxying tornado server in Serve post-processor
use local reveal.js url prefix by default

CDN redirect is handled by the Serve post-processor if necessary
ESC should be handled by CM if tooltip is not on
Have remove_and_cancel_tooltip() return a boolean
converted multi-context with-statements to nested (2.6 compatibility)
moved DummyMod to proper namespace to enable pickling
Revert "converted multi-context with-statements to nested (2.6 compatibility)"

This reverts commit 311acdf45e9d164ac3dd3eb72b913dfc7d7e4314.
update version-check message in setup.py and IPython.__init__

clearer message that IPython no longer supports 2.6.