New formula boxbackup

Box Backup is an open source, completely automatic, on-line backup system.

My first formula, so please review extra-carefully. There are 3 issues that I could't elegantly fix myself:
 - --mandir is somehow ignored, I had to replace some inreplaces to fix this
 - an extra plist file is copied, I had to manually remove it (see comment in formula)
 - the generated caveats are wrong (see text in my caveat)

Thanks!