Add test that a failing ast_transformer is unregistered.
Fix warning message for unregistering AST transformers.
Fix IPython.utils.warn API so messages are automatically displayed followed by a newline.
Add failing test for variable expansion with self (reopened issue #1878).
Fix variable expansion on 'self'

Closes gh-1878 (again)
Merge pull request #2302 from takluyver/i1878-again

Fix variable expansion on 'self'
RemoteError._render_traceback_ calls self.render_traceback

rather than an alias

There are two options here:

1. `_render_traceback_`  should *call* render_traceback
2. any subclass that redefines render_traceback must also redefine `_render_traceback_`

I went with 1., which is more efficient code-wise when subclassing RemoteError
(would prevent future cases of this same mistake),
but less efficient execution-wise, because it involves an extra function call.

closes #2303
test Composite/RemoteError tracebacks
Add welcome_message option to enable_pylab

This way, custom apps that enable pylab won't see it by default.  See for
example sympy/sympy#1489.
always perform requested trait assignments

Some assignments do not change *value*, but do change the object,
and these should not be ignored.

For instance, container objects are currently impossible to assign
if they evaluate as equal.
Added bracket matching for code cells
test Dict trait assignment
fix for issue #2316; adding cluster_id to parallel.Client.__init__
empty string should not be inserted
Merge pull request #2308 from asmeurer/pylab-message

Add welcome_message option to enable_pylab
Merge pull request #2184 from jasongrout/store-history

Expose store_history to execute_request messages.
Merge pull request #2300 from benjiec/master

bug fix: was crashing when sqlite3 is not installed
Add image message handler in ZMQTerminalInteractiveShell

This change introduces handler for messages which contain image in
ZMQTerminalInteractiveShell.  This is useful, for example, when
connecting to the kernel in which pylab inline backend is activated.
Current image handler only supports PIL backend.
Use io.BytesIO instead of StringIO
Add more image handler backends

Also, trait of the image_handler configuration variable is changed to
Enum.