Changes to support gmpy 1.13 or later, or gmpy2 2.0.0b4 or later.
Improvements to gmpy and gmpy2 fixes.
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
3083_not:Changes
3083_not:changed args to arg
3083_not: Rectified a mistake of previous commit- arg.arg changed to arg.args
I hope it is correct now.
edit docstrings
solve: Return all independent solutions (underdetermined systems).
solve: handle Matrix equations.

If we have a Matrix equation Eq(A*B, C), it is transformed into a
system [A*B - C]. We need to iterate over the elements of the matrix
A*B - C again, turning the Matrix equation into a system of equations.

Fixes issue 771: Matrix equations
http://code.google.com/p/sympy/issues/detail?id=771
Incorrect Exception in dsolve()
Travis: install gmp before installing gmpy