Checking that xargo isn't already installed before trying to install it - should prevent the bootstrap script erroring out in an ugly way.

bootstrap.sh

@@ -461,7 +461,11 @@ boot()
 	echo "Cloning github repo..."
 	git clone https://github.com/redox-os/redox.git --origin upstream --recursive
 	rustInstall
+	if [[ "`cargo install --list`" != *"xargo"* ]]; then
 		cargo install xargo
+	else
+		echo "You have xargo installed already!"
+	fi
 	echo "Cleaning up..."
 	rm bootstrap.sh
 	echo