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_()
Added working speaker notes for slides.
Fixing docs.
Fixing info in trailets.
Fixing names for aliases.
skip tests when display variable is not set
fix failing tests without X in IPython.lib

note that pylab_not_importable appears to not be enough to catch if
we're running X. I'm able to import pylab, and it's only %%matplotlib
magic that causes these tests to die
Fixed trailets help.
"use strict" in most (if not all) our javascript

+ fix one variable leaking in global nameespace
use get, for when DISPLAY variable isn't defined
Drop 2.6 and 3.2 from Travis tests
Remove extra assert methods needed for Python 2.6
Update docs for Python version support
Drop nested() function for context managers
Remove _total_seconds helper function
Remove Python 2.6 workaround
remove workaround for 2.6 support
Fixed doc about using PR-related aliases.
irunner use python -m IPython to launch subprocess with matching interpreter

Closes gh-4013