UTF-16-BE and UTF-16-LE external formats were returning the incorrect

number of octets for surrogate pairs.  Two was returned instead of
four.

 * src/pcl/simple-streams/external-formats/utf-16-be.lisp:
 * src/pcl/simple-streams/external-formats/utf-16-le.lisp:
   * Return correct number of octets
 * src/general-info/release-20d.txt
   * Update.