Check for docker-squash and the correct netgo libs in the makefile.

Makefile

@@ -13,12 +13,24 @@ SCOPE_UI_BUILD_EXPORT=scope_ui_build.tar
 SCOPE_UI_BUILD_IMAGE=$(DOCKERHUB_USER)/scope-ui-build
 GIT_REVISION=$(shell git rev-parse HEAD)
 
+ifeq ("$(DOCKER_SQUASH)","")
+$(error Please install docker-squash by running 'make dep')
+endif
+
 all: $(SCOPE_EXPORT)
 
 $(SCOPE_EXPORT): $(APP_EXE) $(PROBE_EXE) docker/*
 	cp $(APP_EXE) $(PROBE_EXE) docker/
 	$(SUDO) docker build -t $(SCOPE_IMAGE) docker/
-	$(SUDO) docker save $(SCOPE_IMAGE):latest | $(SUDO) $(DOCKER_SQUASH) -t $(SCOPE_IMAGE) | tee $@ | $(SUDO) docker load
+	$(SUDO) docker save $(SCOPE_IMAGE):latest | sudo $(DOCKER_SQUASH) -t $(SCOPE_IMAGE) | tee $@ | $(SUDO) docker load
+	 @strings $@ | grep cgo_stub\\\.go >/dev/null || { \
+	        rm $@; \
+	        echo "\nYour go standard library was built without the 'netgo' build tag."; \
+	        echo "To fix that, run"; \
+	        echo "    sudo go clean -i net"; \
+	        echo "    sudo go install -tags netgo std"; \
+	        false; \
+	    }
 
 $(APP_EXE): app/*.go report/*.go xfer/*.go