latex(): Separate numbers with \cdot by default.

Fixes issue 3740: Don't use \times in latex
http://code.google.com/p/sympy/issues/detail?id=3740
latex(): Print True/False as latex mathrm.

Also prevent IPython from printing True/False as latex at all.

Fixes issue 3757: True and False in latex
http://code.google.com/p/sympy/issues/detail?id=3757
latex(): Add empty {} argument to array printing.

Fixes issue 3861: latex(Matrix, mat_str='array') misses first element
http://code.google.com/p/sympy/issues/detail?id=3861
Implementation of the second heuristic

The second heuristic is a method to find the infinitesimals xi and eta of
the PDE mentioned in the documentation under infinitesimals

There are four assumptions to xi and eta

1. eta = 0, xi = f(x)*g(y)
2. eta = 0, xi = g(x)*f(y)
3. xi = 0, eta = f(y)*g(x)
4. xi = 0, eta = f(x)*g(y)

g is a function got by extracting factors from the numerator and denominator
f is the function got by solving the auxilliary ODE obtained after
substituting g in the PDE. For now, it is assumed f can be obtained if
the auxilliary ode obtained is separable in f
3722: more advanced re/im support
Fix issue 3890: dsolve failing for an equality multiplied by -1
http://code.google.com/p/sympy/issues/detail?id=3890

One issue was the reordering or args, which should not happen
for Tuple instances, and another issue was the unneeded call
to piecewise_fold.
Fix LaTeX printing bug for Chi.
Add dsolve test for issue 3890.
Added Seshagiri Prabhu to AUTHORS/aboutus. Welcome to SymPy!
Merge pull request #2167 from jrioux/printing

LaTeX printing bug hunt
rework real/imag processing; remove dup symbols
Add a comment about the handling of Piecewise.
Wrap long lines.
Remove e.is_Add branch in limit():

    This should fix issues, like mentioned in
    https://groups.google.com/forum/?fromgroups=#!topic/sympy/61pRw1PINUA
    or issues 2641 and 3461.
test for limit(Sum(1/x, (x, 1, y)) - 1/y, y, oo), now raises NotImplementedError
Add XFAIL test for issue 3744
Tests for issues 3461 and 2641
Merge pull request #2183 from smichr/auth

Added Seshagiri Prabhu to AUTHORS/aboutus. Welcome to SymPy!
Merge pull request #2178 from smichr/solve

3722: more advanced re/im support
Rewrite using expr.has(*symbols).