Use readline.columns in sys.inspect when possible

Though, this should probably be an option to sys.inspect and be set by REPL.

lib/sys.js

@@ -230,7 +230,7 @@ exports.inspect = function (obj, showHidden, depth, colors) {
         return prev + cur.length + 1;
       },0);
 
-    if (length > 50) {
+    if (length > (require('readline').columns || 50)) {
       output = braces[0]
              + (base === '' ? '' : base + '\n ')
              + ' '