TST: sparse: add explicit zeros to matrices used in noncanonical format tests

(cherry picked from commit 02c072b765dac219880197a0f8dea0f012e8c4e4)
TST: sparse: dense RHS/LHS are supported in comparisons for Numpy >= 1.8, so enable the tests

(cherry picked from commit 5470d0d18fed8162ad83883517b0150297d3e7ac)
BUG: sparse: fix bugs in __eq__ with explicit zeros, and fix nan comparisons

(cherry picked from commit 4fca50bf627adbaefadccb20e89e0f93615a01db)