Fix sys.path missing '' as first entry in ipython kernel.

[bfroehle]

The comment is copied from the corresponding code in TerminalIPythonApp.

Closes #1240.

As Min suggests in #1240, we should consider gathering up all of these lines and putting them into InteractiveShell (or InteractiveShellApp?) instead.

To test:

$ ipython kernel &
[1] 10069
$ ipython console --existing kernel-10035.json
Python 2.7.3 (default, Apr 20 2012, 22:39:59) 
Type "copyright", "credits" or "license" for more information.

IPython 0.13.dev -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: import sys

In [2]: sys.path[0]
Out[2]: ''

[minrk]

Can you put it in InteractiveShellApp? That way possible new entry points will inherit this properly.

[bfroehle]

Yes, I considered that, however it wasn't really clear where it would belong. I'll look again when I get a chance.

[minrk]

If nowhere seems obvious, just add a separate init_path() step with this one line, and call it from initialize().

[bfroehle]

Tested to have the desired behavior (sys.path[0] == '' and sys.path[1] != '') in:

• ipython
• ipython console
• ipython qtconsole
• ipython notebook
• ipython kernel + ipython console --existing <...>

[minrk]

Terrific, thanks! I'll go ahead and merge.