exclude given directories in recursive mode

[Motardo]

This addresses issue #8 - It allows you to write commands like: fdupes -e./.git -r . or fdupes --exclude-dir=foo/bar -r foo. It uses sys/queue.h for the linked list implementation to hold the names of directories that should be ignored.

[george-viaud]

This is a much needed feature - I see there are conflicts though and I've not the time or experience to resolve them (unfortunately for me). Anyone care to take this up? @adrianlopezroche thank you for the wonderful tool - any chance this pull can be worked into the next build? I'm not sure how active this project is but it's a very worth tool indeed, this feature would make it much more powerful. Thanks