latex(Mul()): Deal with integer coeff.
latex(Mul()): Deal with short and long fractions.

- Print short fractions as p/q
- Print long fractions as \frac{p1}{q} (p2), where p1 is a coeff
  and p2 is e.g. an Add.
Implement and use _needs_mul_brackets.

This is used to determine if a term appearing in a Mul needs to
have surrounding brackets or not.
Some simplifications and comments.
Use mul_symbol instead of a space as separator.
Render the allowed numer/denom ratio for long fractions customizable.
fold_short_frac defaults to True for inline and False otherwise.
Let _print_Mul handle expr raised to negative powers.

Fixes issue 2576: latex(1/x**2) should return a \frac
http://code.google.com/p/sympy/issues/detail?id=2576
Add latex printing tests for fractions.
latex(Mul()): Don't special-case coeff.

Print x/2 as \frac{x}{2} instead of \frac{1}{2} x. This makes it
consistent with str and pretty printers and simplify the code
quite a bit.
Refine needs_mul_brackets.

Use expr.has() instead of isinstance to account for e.g.
Mul(2, Integral(x, x)) which needs brackets.
doctester: support comparison of floating point numbers
fix travis failures: floats with more than one leading dot are not allowed
automatically import some future imports for all doctests
float parser: support complex numbers and floats in scientific notation
unskipped several doctests
moving imports of numpy (and matplotlib/mpl_toolkits) out of module scope and into functions/classes
reduces the import time of sympy by 50-75%.

See discussion at https://code.google.com/p/sympy/issues/detail?id=3427
add mpl_toolkits.mplot3d import to section of MatplotlibBackend for 3d plotting
manualintegrate: handle unevaluated derivatives
Merge pull request #2140 from hacman/numpy_import

moving imports of numpy (and matplotlib/mpl_toolkits) out of module scope...