Abort build if working directory contains spaces - not supported by (at least) debootstrap and cdebootstrap.

helpers/lh_build

@@ -35,6 +35,12 @@ then
 	exit 1
 fi
 
+if echo $(pwd) | grep -qs " "
+then
+	Echo_error "Cannot build live image from a directory containing spaces"
+	exit 1
+fi
+
 # Bootstrapping system
 lh_bootstrap ${*}