Update Random to create a per-instance copy of the RNG

Before this change, it appeared that multiple, independent Faker
instances were legal.  But, when multiple instances were created, their
shared random number generators would overwrite each others' states.

After this change, each Random instance (and therefore each Faker
instance) has its own copy of the random number generator, ensuring that
calls to one Faker instance do not affect the stream of values generated
by another.

lib/random.js

@@ -5,15 +5,27 @@ var mersenne = require('../vendor/mersenne');
  * @namespace faker.random
  */
 function Random (faker, seed) {
+  var gen = new mersenne.MersenneTwister19937();
+
   // Use a user provided seed if it exists
   if (seed) {
     if (Array.isArray(seed) && seed.length) {
-      mersenne.seed_array(seed);
+      gen.init_by_array(seed);
     }
     else {
-      mersenne.seed(seed);
+      gen.init_genrand(seed);
     }
   }
+
+  // Copied from the marsenne package for compatibility.
+  function rand(max, min) {
+    if (max === undefined) {
+      min = 0;
+      max = 32768;
+    }
+    return Math.floor(gen.genrand_real2() * (max - min) + min);
+  }
+
   /**
    * returns a single random number based on a max number or range
    *
@@ -48,7 +60,7 @@ function Random (faker, seed) {
     }
 
     var randomNumber = Math.floor(
-      mersenne.rand(max / options.precision, options.min / options.precision));
+      rand(max / options.precision, options.min / options.precision));
     // Workaround problem in Float point arithmetics for e.g. 6681493 / 0.01
     randomNumber = randomNumber / (1 / options.precision);
 

test/random.unit.js

@@ -3,6 +3,7 @@ if (typeof module !== 'undefined') {
     var sinon = require('sinon');
     var _ = require('lodash');
     var faker = require('../index');
+    var Faker = require('../lib');
 }
 
 
@@ -189,4 +190,19 @@ describe("random.js", function () {
       assert.ok(hex.match(/^(0x)[0-9a-f]+$/i));
     })
   })
+
+  describe('independent', function() {
+
+    it('generates independent sequences', function () {
+      var faker1 = new Faker();
+      faker1.seed(1);
+
+      var faker2 = new Faker();
+      faker2.seed(1);
+
+      assert.equal(faker1.random.number(), faker2.random.number());
+    })
+
+  })
+
 });