* New primop builtins.filterSource, which can be used to filter files

from a source directory.  All files for which a predicate function
  returns true are copied to the store.  Typical example is to leave
  out the .svn directory:

    stdenv.mkDerivation {
      ...
      src = builtins.filterSource
        (path: baseNameOf (toString path) != ".svn")
        ./source-dir;
      # as opposed to
      #   src = ./source-dir;
    }

  This is important because the .svn directory influences the hash in
  a rather unpredictable and variable way.

src/libstore/local-store.hh

@@ -50,7 +50,8 @@ public:
     void queryReferrers(const Path & path, PathSet & referrers);
 
     Path addToStore(const Path & srcPath, bool fixed = false,
-        bool recursive = false, string hashAlgo = "");
+        bool recursive = false, string hashAlgo = "",
+        PathFilter & filter = defaultPathFilter);
 
     Path addTextToStore(const string & suffix, const string & s,
         const PathSet & references);