TST tests for non-canonical input to sparse matrix operations
TST correct logic for noncanonical sparse tests
TST add known failures for non-canonical sparse matrices
TST fix tests to avoid negating unsigned datatypes
TST use assert_allclose instead of _array_equal
Merge pull request #3254 from jnothman/test_noncanonical_sparse

TST: sparse: tests for non-canonical input to sparse matrix operations

A number of sparse matrix formats are designed to treat duplicate values
as their sum; they prefer indices in sorted order, but should be capable
when unsorted. The current test suite largely compares functionality to
numpy arrays/matrices, and so constructs sparse matrices from those,
producing only canonical sparse forms.

These commits introduce tests for non-canonical forms.