Make Samba4 Heimdal symbols renaming more correct and stable.

 * Take data symbols (D) in accout as well as code ones (T);
 * After adding -U to diff(1)'s command line, extra.conflicts is not
   needed anymore;
 * Add a few more items SAFE_SYMBOLS;
 * No need for -r option when invoking sort(1), actually;
 * Add "|| true" after calling diff, to avoid early exit from
   subshell;
 * Reformat a few command blocks, making them easier to be read.