Changes to support gmpy 1.13 or later, or gmpy2 2.0.0b4 or later.
Improvements to gmpy and gmpy2 fixes.
Remove two extraneous lines from logic to detect gmpy/gmpy2 version.
slice of slices simplify
MatrixSlice X[2] -> X[2, :] required
negative indices for MatrixSlice
Travis: install gmp before installing gmpy
Merge pull request #1787 from mrocklin/matrix-slice-of-slice

slice of MatrixSlices simplify
Merge pull request #1805 from certik/travis_gmpy

Travis: install gmp before installing gmpy
Merge pull request #1766 from casevh/master

Single patch for gmpy and gmpy2 support.