LFW: Improve error message for missing pairs.txt
LFW: Improve error message for missing pairs.txt

nmabhi/Webface,Alexx-G/openface,xinfang/face-recognize,francisleunggie/openface,Alexx-G/openface,xinfang/face-recognize,Alexx-G/openface,nhzandi/openface,francisleunggie/openface,cmusatyalab/openface,Alexx-G/openface,nmabhi/Webface,nhzandi/openface,nmabhi/Webface,francisleunggie/openface,cmusatyalab/openface,nmabhi/Webface,cmusatyalab/openface,nhzandi/openface,xinfang/face-recognize