added list_mean() to allow nested_cv with multiple performance measures
added list_mean() to allow nested_cv with multiple performance measures

claesenm/optunity,MarkAWard/optunity,MarkAWard/optunity,chrinide/optunity,claesenm/optunity,MarkAWard/optunity,chrinide/optunity,MarkAWard/optunity,chrinide/optunity,chrinide/optunity,claesenm/optunity,claesenm/optunity