Escape backspace in regexp classes as "\b", not "\x08"

The "\x08" escaping is necessary only outside of classes (where "\b"
means "word boundary").

lib/compiler/js.js

@@ -36,17 +36,18 @@ var js = {
      * For portability, we also escape all control and non-ASCII characters.
      */
     return s
-      .replace(/\\/g, '\\\\')   // backslash
-      .replace(/\//g, '\\/')    // closing slash
-      .replace(/\]/g, '\\]')    // closing bracket
-      .replace(/\^/g, '\\^')    // caret
-      .replace(/-/g,  '\\-')    // dash
-      .replace(/\0/g, '\\0')    // null
-      .replace(/\t/g, '\\t')    // horizontal tab
-      .replace(/\n/g, '\\n')    // line feed
-      .replace(/\v/g, '\\v')    // vertical tab
-      .replace(/\f/g, '\\f')    // form feed
-      .replace(/\r/g, '\\r')    // carriage return
+      .replace(/\\/g,   '\\\\')   // backslash
+      .replace(/\//g,   '\\/')    // closing slash
+      .replace(/\]/g,   '\\]')    // closing bracket
+      .replace(/\^/g,   '\\^')    // caret
+      .replace(/-/g,    '\\-')    // dash
+      .replace(/\0/g,   '\\0')    // null
+      .replace(/\x08/g, '\\b')    // backspace
+      .replace(/\t/g,   '\\t')    // horizontal tab
+      .replace(/\n/g,   '\\n')    // line feed
+      .replace(/\v/g,   '\\v')    // vertical tab
+      .replace(/\f/g,   '\\f')    // form feed
+      .replace(/\r/g,   '\\r')    // carriage return
       .replace(/[\x00-\x0F]/g,          function(ch) { return '\\x0' + hex(ch); })
       .replace(/[\x10-\x1F\x7F-\xFF]/g, function(ch) { return '\\x'  + hex(ch); })
       .replace(/[\u0100-\u0FFF]/g,      function(ch) { return '\\u0' + hex(ch); })