DadaIMC usermedia dir whitelist

A whitelist for the usermedia-dir on DadaIMC installations. For background info, check this post.

• whitelist.txt - this should be put into the apache config or a .htaccess file in the base directory. this file is hardlinked against the indymedia.se install and should always be up to date.
• whitelist.pl.txt - the perl script that generate the above file. if your imc need to support more filetypes they can be easily added.