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
Changes to support gmpy 1.13 or later, or gmpy2 2.0.0b4 or later.
Improvements to gmpy and gmpy2 fixes.
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
Added support for Poly(f, x, y).coeff(x*y)
update coeff-related docstrings; special case Poly in coeff
Remove two extraneous lines from logic to detect gmpy/gmpy2 version.
3083: Not now accepts only one argument
change Poly.coeff to Poly.monomial_coeff
slice of slices simplify
change monomial_coeff to coeff_monomial
MatrixSlice X[2] -> X[2, :] required
solve: return all independent solutions.

Now solve will return all independent solutions instead of breaking
out at the first solution found.
negative indices for MatrixSlice