Reintroduce nnz and nonzeros as discussed in #6769
Deprecate nfilled for SparseMatrixCSC.
Deprecate nonzeros for StridedArray and BitArray.
Deprecate nnz for StridedArray.
Update documentation for structural nonzeros.
Update NEWS
Catch writes to protected memory in mmapped arrays (fix #3434)
Only apply the gemv workaround when OpenBLAS is being used.
Revert "Catch writes to protected memory in mmapped arrays (fix #3434)"

This reverts commit caa4bfa17aeaada0c66f33128e206477842f7eab.
Merge pull request #6978 from lindahua/dh/openblas1

Only apply the gemv workaround when OpenBLAS is being used.
Merge pull request #6963 from JuliaLang/vs/nnz

RFC: Reintroduce nnz and nonzeros