* Removed `build-allow-root'.

* Added `build-users-group', the group under which builds are to be
  performed.
* Check that /nix/store has 1775 permission and is owner by the
  build-users-group.

src/libmain/shared.hh

@@ -24,6 +24,9 @@ namespace nix {
 Path makeRootName(const Path & gcRoot, int & counter);
 void printGCWarning();
 
+/* Whether we're running setuid. */
+bool setuidMode = false;
+
 }