1.0.22.6: some ANSI-STREAM cleanups & micro-optimization

1.0.22.6: some ANSI-STREAM cleanups & micro-optimization

 * Make WRITE-LINE dispatch on the type of the stream only once -- not
   for both writing the string and the newline separately.

 * ANSI-STREAM-WRITE-LINE checks the START and END parameters, so
   callers of %WRITE-LINE don't need to.

 * Remove some redundant type checks from WRITE-LINE and WRITE-STRING
   code paths.

 * SB-IMPL::INDENTING-STREAM was unused, delete it. (Note: update your
   Slime!)