Duplicate Downloads

[tanmahah]

If I run the script with search string twice or more the script appears to download the file again and again, although appending a digit to the file name, as was intended by author.
It will be nice to avoid such copies.
If the file is present in same directory and the url is present in tried urls, we must not download the file.

[ostrolucky]

tried_urls is saved in memory and not persisted between runs, so this is not possible, but I pushed a commit which detects that image is duplicate after it has been downloaded