convert factorials to gamma-function format
adding factorial test case
be more explicit with the rewrite operation
stripping trailing whitespace
adding negative number test case
only rewrite for positive z0
use is_positive in favor of __ge__

relevant issue: http://code.google.com/p/sympy/issues/detail?id=2832
adding symbolic z0 test case for factorials
Travis: enable gmpy tests by default
Fix whitespace error introduced by #1812
Merge pull request #1807 from certik/travis_enable

Travis: enable gmpy tests by default
Merge pull request #1734 from perimosocordiae/master

Fix for #1733: mishandling of factorials when taking limits
Add CJ Carey to the AUTHORS/aboutus. Welcome to SymPy!
Factors accepts Expr; as_powers_dict returns int-based defaultdict

`as_powers_dict` didn't play nicely with Factors because for Mul,
a list-based defaultdict was returned. It now returns an int-based
one like Add does.

Docstrings for exprtools Factors were added.

distinguish between 0 and 1 factors

make repr canonical
add is_zero and is_one properties to Factors
watch for -Rational and nc in Factors
watch for I in Factors
fix exprtools for Python 2.5
add fu to simplify
fix doctests and order terms