getwallpaper: Add nitrogen support

fetch

@@ -962,7 +962,11 @@ getvisualstyle () {
 getwallpaper () {
     case "$os" in
         "Linux" | *"BSD")
-            img="$(awk -F\' '/feh/ {printf $2}' $HOME/.fehbg)"
+            if type -p feh >/dev/null 2>&1; then
+                img="$(awk -F\' '/feh/ {printf $2}' "$HOME/.fehbg")"
+            elif type -p nitrogen >/dev/null 2>&1; then
+                img="$(awk -F'=' '/file/ {printf $2}' "$HOME/.config/nitrogen/bg-saved.cfg")"
+            fi
         ;;
 
         "Mac OS X")