What I'd like to be able to do, instead, is to add exceptions to the blacklist. For instance
I would like to install the header files from R.framework (r-base) in rkward, while still
excluding all other headers (as defined in the default blacklist).

In existing blueprints, the whitelist feature seems to be unused. (quassel ships a whitelist.txt,
but for all I can see it is never read).

"Whitelisted files only"-behavior can be achieve by having "^.*$" in the blacklist, with this patch.