Fix ticket:58. Handle the BOM character for utf-16 and utf-32. This

is a bit of a hack.

 * src/code/stream.lisp:
  * Check the state to see if a BOM was read.  This critically depends
    on knowing the format of the state variable for utf16 and utf32
    formats, but the stream code shouldn't have to know the state
    internals. 

 * src/general-info/release-20d.txt
   * Update.