vl_roc.m: improve the documentation and fix the AUC computation for the ‘fptn’ variant of the plot
vl_roc.m: improve the documentation and fix the AUC computation for the ‘fptn’ variant of the plot

erexhepa/vlfeat,vlfeat/vlfeat,j-bo/vlfeat,vlfeat/vlfeat,rxl194/vlfeat,j-bo/vlfeat,richarddzh/vlfeat,erexhepa/vlfeat,cvfish/vlfeat,WangDequan/vlfeat,erexhepa/vlfeat,CansenJIANG/vlfeat,hongzhili/vlfeat,vlfeat/vlfeat,cvfish/vlfeat,j-bo/vlfeat,CansenJIANG/vlfeat,qubick/vlfeat,hongzhili/vlfeat,hongzhili/vlfeat,cvfish/vlfeat,CansenJIANG/vlfeat,j-bo/vlfeat,j-bo/vlfeat,hongzhili/vlfeat,richarddzh/vlfeat,cvfish/vlfeat,WangDequan/vlfeat,CansenJIANG/vlfeat,qubick/vlfeat,mylxiaoyi/vlfeat,qubick/vlfeat,mylxiaoyi/vlfeat,qubick/vlfeat,vlfeat/vlfeat,rxl194/vlfeat,mylxiaoyi/vlfeat,rxl194/vlfeat,qubick/vlfeat,erexhepa/vlfeat,WangDequan/vlfeat,CansenJIANG/vlfeat,CansenJIANG/vlfeat,WangDequan/vlfeat,rxl194/vlfeat,hongzhili/vlfeat,richarddzh/vlfeat,vlfeat/vlfeat,mylxiaoyi/vlfeat,qubick/vlfeat,WangDequan/vlfeat,mylxiaoyi/vlfeat,vlfeat/vlfeat,WangDequan/vlfeat,cvfish/vlfeat,hongzhili/vlfeat,erexhepa/vlfeat,mylxiaoyi/vlfeat,richarddzh/vlfeat,richarddzh/vlfeat,rxl194/vlfeat,cvfish/vlfeat,richarddzh/vlfeat,rxl194/vlfeat,erexhepa/vlfeat