fix #8968: abs(big(-0.0))

backport of a42a54bf5ba439850d4d78dc013c397e49cac79b
Fix bug in issym(A::BitMatrix)

numnz -> countnz

backport of 7ba14fe8dc25286df86c03c10f5d3d9260558254

Add issym test for bitarrays

backport of 85b015f8dfc089698db3904a89a25b14d49552f7