mfabinski

fix #52 by adding the specific exception handler in the inner exception handling block. Now the update flag works as supposed: ``` matthias@seth:~/git/RedditImageGrab$ python redditdl.py cats ~/Bilder/cats --num 5 --update...

The --update flag should abort the downloading, if one already downloaded image should be downloaded again. In this case the script should abort the download. The exception handler for FileExistsException...