Add `rar` command to `extract` function.

This addition tries to use the `rar` command, if `unrar` isn't found.

modules/archive/functions/extract

@@ -53,7 +53,7 @@ while (( $# > 0 )); do
     (*.lzma) unlzma "$1" ;;
     (*.Z) uncompress "$1" ;;
     (*.zip) unzip "$1" -d $extract_dir ;;
-    (*.rar) unrar e -ad "$1" ;;
+    (*.rar) unrar e -ad "$1" || rar e -ad "$1" ;;
     (*.7z) 7za x "$1" ;;
     (*.deb)
       mkdir -p "$extract_dir/control"