Add equality operators to maybe_nul_ret
Add equality operators to maybe_nul_ret

matus-chochlik/GSL,john-lynch/GSL,vladon/GSL,eteran/GSL,nguarracino/GSL,trebconnell/GSL,kernhanda/GSL,jbcoe/GSL,s8435330song/GSL,martinmoene/GSL,bashrc-real/GSL,Josaphat/GSL,kevgs/GSL,garyfurnish/GSL,neilmacintosh/GSL