Fix init_session(ipython=False) for non-unicode terminals.

InteractiveConsole is another case were we should not force
use_unicode=True. Instead, let's rely on the code that checks
sys.stdout.encoding to automatically set this to the correct
value.
init_printing: Update a comment.
Make the default color of LaTeX printing black instead of blue
3826: reverse tan double angle
Constant coeff general linear PDE's- first commit
Added references
Rebased and corrected test failure
Implementing TODO 1 and 4- first pass
Hopefully done with all TODO's
issue 3434: warnings from matplotlib when starting isympy
the issue was that matplotlib.pyplot was being imported before
pylab was initialized. initializing pylab after the import of
matplotlib.pyplot caused a warning to be printed to the console.
some plotting methods don't work in py3k without this. objects are making
their way into sympy's cache.
hack to get the pyplot fix to work with matplotlib/py3k
unit tests to ensure that interval objects in the plotting module are hashable
this came up in issue 3434
add comment and tests, remove/reformat some old comments
amend test for case where matplotlib is not installed
3821: simplify trig to exp and vice versa

recognizing I*tan(x) and tanh(x) will take a little more work
factor exptrigsimp out of simplify
update exptrigsimp docs
clarify regression test
Merge pull request #30 from sn6uv/exptrigsimp

factor exptrigsimp out of simplify