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.
Merge pull request #1992 from jrioux/printing

TeX printing of fractions.