Use 11-bit mask in Bloom.check (fixes ethereumjs#303)

Author: gkaemmer

lib/bloom.js

@@ -42,7 +42,7 @@ Bloom.prototype.add = function (e) {
  */
 Bloom.prototype.check = function (e) {
   e = utils.sha3(e)
-  var mask = 511 // binary 111111111
+  var mask = 2047 // binary 11111111111
   var match = true
 
   for (var i = 0; i < 3 && match; i++) {