buffer: introduce latin1 encoding term

When node began using the OneByte API (f150d56) it also switched to
officially supporting ISO-8859-1. Though at the time no new encoding
string was introduced.

Introduce the new encoding string 'latin1' to be more explicit. The
previous 'binary' and documented as an alias to 'latin1'.  While many
tests have switched to use 'latin1', there are still plenty that do both
'binary' and 'latin1' checks side-by-side to ensure there is no
regression.

PR-URL: https://github.com/nodejs/node/pull/7111
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/string_decoder.js

@@ -19,6 +19,7 @@ function normalizeEncoding(enc) {
         return 'utf16le';
       case 'base64':
       case 'ascii':
+      case 'latin1':
       case 'binary':
       case 'hex':
         return enc;
@@ -225,7 +226,7 @@ function base64End(buf) {
   return r;
 }
 
-// Pass bytes on through for single-byte encodings (e.g. ascii, binary, hex)
+// Pass bytes on through for single-byte encodings (e.g. ascii, latin1, hex)
 function simpleWrite(buf) {
   return buf.toString(this.encoding);
 }