VlFeatCovdet.m: simplifies and adapts to new implementation of covdet
VlFeatCovdet.m: simplifies and adapts to new implementation of covdet

vlfeat/vlbenchmarks,andersbll/vlbenchmarks,andersbll/vlbenchmarks,andersbll/vlbenchmarks,CVML/vlbenchmarks,CVML/vlbenchmarks,vlfeat/vlbenchmarks,CVML/vlbenchmarks,vlfeat/vlbenchmarks,andersbll/vlbenchmarks