* Operation `--delete-generations' to delete generations of a

profile.  Arguments are either generation number, or `old' to delete
  all non-current generations.  Typical use:

  $ nix-env --delete-generations old
  $ nix-collect-garbage

* istringstream -> string2Int.

src/libutil/util.hh

@@ -246,6 +246,10 @@ string statusToString(int status);
 bool statusOk(int status);
 
 
+/* Parse a string into an integer. */
+bool string2Int(const string & s, int & n);
+
+
 /* !!! HACK HACK HACK - this should be in shared.hh, but it's to
    facilitate a quick hack - will remove this eventually (famous last
    words). */