Save jpg-images for detector demo if used flag: -prefix <filename>

AlexeyAB

2018-05-21 b88b7b645bc71ddcd83f81744c78419e0ed15078

 build/darknet/x64/cfg/yolov3.cfg

@@ -610,7 +610,7 @@
classes=80
num=9
jitter=.3
ignore_thresh = .5
ignore_thresh = .7
truth_thresh = 1
random=1

@@ -696,7 +696,7 @@
classes=80
num=9
jitter=.3
ignore_thresh = .5
ignore_thresh = .7
truth_thresh = 1
random=1

@@ -783,7 +783,7 @@
classes=80
num=9
jitter=.3
ignore_thresh = .5
ignore_thresh = .7
truth_thresh = 1
random=1