Include beforeEach hooks in --slow timings

Previously `beforeEach` hook runtimes were excluded from test times. This is
misleading, since `beforeEach` hooks can take a significant amount of time.
It's better to report this accurately, especially since `beforeEach` hook costs
are not amortized over every test (like `before` hooks are).

lib/runnable.js

@@ -289,7 +289,12 @@ Runnable.prototype.globals = function(globals) {
  */
 Runnable.prototype.run = function(fn) {
   var self = this;
-  var start = new Date();
+  var start;
+  if (typeof self.start === 'number') {
+    start = self.start;
+  } else {
+    start = Date.now();
+  }
   var ctx = this.ctx;
   var finished;
   var emitted;

lib/runner.js

@@ -501,6 +501,7 @@ Runner.prototype.parents = function() {
 Runner.prototype.runTest = function(fn) {
   var self = this;
   var test = this.test;
+  test.start = self.start;
 
   if (!test) {
     return;
@@ -623,6 +624,7 @@ Runner.prototype.runTests = function(suite, fn) {
     }
 
     // execute test and hook(s)
+    self.start = Date.now();
     self.emit(constants.EVENT_TEST_BEGIN, (self.test = test));
     self.hookDown(HOOK_TYPE_BEFORE_EACH, function(err, errSuite) {
       if (test.isPending()) {