* 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/remote-store.cc

@@ -213,7 +213,7 @@ void RemoteStore::queryReferrers(const Path & path,
 
 
 Path RemoteStore::addToStore(const Path & _srcPath, bool fixed,
-    bool recursive, string hashAlgo)
+    bool recursive, string hashAlgo, PathFilter & filter)
 {
     Path srcPath(absPath(_srcPath));
     
@@ -222,7 +222,7 @@ Path RemoteStore::addToStore(const Path & _srcPath, bool fixed,
     writeInt(fixed ? 1 : 0, to);
     writeInt(recursive ? 1 : 0, to);
     writeString(hashAlgo, to);
-    dumpPath(srcPath, to);
+    dumpPath(srcPath, to, filter);
     processStderr();
     Path path = readStorePath(from);
     return path;