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.
codeprinters: fix Rational's printing for code (as fractions of doubles)

S(4)/3 * x -> (4.0/3.0)*x for ccode, not 4*x/3
ccode: print Rational numbers with long double
printing.rst: fix doctest failures for fcode
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
Merge branch 'master' into rationals-printing-in-code
Added support for Poly(f, x, y).coeff(x*y)
update coeff-related docstrings; special case Poly in coeff
Merge branch 'master' into rationals-printing-in-code
added a recursive doit() call in Sum

This enables the evaluation of nested sums.
doc string revesion for Sum
Remove two extraneous lines from logic to detect gmpy/gmpy2 version.