chore(log): add `log.empty()`  method to the testing logger

`log.empty()` is the same as `log.reset()`, except thati `empty()`  also returns the current array with messages

instead of:

```
// do work
expect(log).toEqual(['bar']);
log.reset();
```

do:

```
// do work
expect(log.empty()).toEqual(['bar']);
```
fix(Scope): $watchCollection should call listener with oldValue

Originally we destroyed the oldValue by incrementaly copying over portions of the newValue
into the oldValue during dirty-checking, this resulted in oldValue to be equal to newValue
by the time we called the watchCollection listener.

The fix creates a copy of the newValue each time a change is detected and then uses that
copy *the next time* a change is detected.

To make `$watchCollection` behave the same way as `$watch`, during the first iteration
the listener is called with newValue and oldValue being identical.

Since many of the corner-cases are already covered by existing tests, I refactored the
test logging to include oldValue and made the tests more readable.

Closes #2621
Closes #5661
Closes #5688
Closes #6736
feat($compile): add support for $observer deregistration

In order to make the behavior compatible with $rootScope.$watch and $rootScope.$on methods, and
make it possible to deregister an attribute observer, Attributes.$observe method now returns a
deregistration function instead of the observer itself.

BREAKING CHANGE: calling attr.$observe no longer returns the observer function, but a
    deregistration function instead.

    To migrate the code follow the example below:

    Before:

```
    directive('directiveName', function() {
      return {
        link: function(scope, elm, attr) {
          var observer = attr.$observe('someAttr', function(value) {
            console.log(value);
          });
        }
      };
    });
```

    After:

```
    directive('directiveName', function() {
      return {
        link: function(scope, elm, attr) {
          var observer = function(value) {
            console.log(value);
          };

          attr.$observe('someAttr', observer);
        }
      };
    });
```

Closes #5609
feat(ngMock.$httpBackend): added support for function as URL matcher

It's now possible to pass a function to match the URL in $httpBackend mocked
expectations. This gives a more sophisticate control over the URL matching
without requiring complex RegExp mantainance or the workaround of creating
an object with a `test` function in order to mimic RegExp interface.

This approach was suggested in [this
thread](https://groups.google.com/d/msg/angular/3QsCUEvvxlM/Q4C4ZIqNIuEJ)

Closes #4580
style(ngMocks): remove ws
docs(tutorial/step_05): removed stray "a"
docs(tutorial/step_05): fix services link
fix($$RAFProvider): check for webkitCancelRequestAnimationFrame

Android 4.3 only supports webkitCancelRequestAnimationFrame.

Closes #6526
fix($httpBackend): don't error when JSONP callback called with no parameter

This change brings Angular's JSONP behaviour closer in line with jQuery's. It will no longer treat
a callback called with no data as an error, and will no longer support IE8 via the onreadystatechanged
event.

BREAKING CHANGE:

Previously, the JSONP backend code would support IE8 by relying on the readystatechanged events. This
is no longer the case, as these events do not provide adequate useful information for deeming whether
or not a response is an error.

Previously, a JSONP response which did not pass data into the callback would be given a status of -2,
and treated as an error. Now, this situation will instead be given a status of 200, despite the lack
of data. This is useful for interaction with certain APIs.

Previously, the onload and onerror callbacks were added to the JSONP script tag. These have been
replaced with jQuery events, in order to gain access to the event object. This means that it is now
difficult to test if the callbacks are registered or not. This is possible with jQuery, using the
$.data("events") method, however it is currently impossible with jqLite. This is not expected to
break applications.

Closes #4987
Closes #6735
fix(ngTouch): update workaround for desktop Webkit quirk

Fix click busting of input click triggered by a label click quickly
following a touch event on a different element, in desktop
and mobile WebKit

To reproduce the issue fixed by this commit set up a page with
 - an element with ng-click
 - a radio button (with hg-model) and associated label
In a quick sequence tap on the element and then on the label.
The radio button will not be checked, unless PREVENT_DURATION has passed

Closes #6302
fix(ngCookie): convert non-string values to string

Previously, non-string values stored in $cookies would be removed, without warning the user, and
causing difficulty debugging. Now, the value is converted to string before being stored, and the
value is not dropped. Serialization may be customized using the toString() method of an object's
prototype.

Closes #6151
Closes #6220
fix(orderBy): support string predicates containing non-ident characters

The orderBy filter now allows string predicates passed to the orderBy filter to make use property
name predicates containing non-ident strings, such as spaces or percent signs, or non-latin
characters.

This behaviour requires the predicate string to be double-quoted.

In markup, this might look like so:

```html
<div ng-repeat="item in items | orderBy:'\"Tip %\"'">
...
</div>
```

Or in JS:

```js
var sorted = $filter('orderBy')(array, ['"Tip %"', '-"Subtotal $"'], false);
```

Closes #6143
Closes #6144
fix(select): avoid checking option element selected properties in render

In Firefox, hovering over an option in an open select menu updates the selected property of option
elements. This means that when a render is triggered by the digest cycle, and the list of options
is being rendered, the selected properties are reset to the values from the model and the option
hovered over changes. This fix changes the code to only use DOM elements' selected properties in a
comparison when a change event has been fired. Otherwise, the internal new and existing option
arrays are used.

Closes #2448
Closes #5994
test(ngMock): workaround issue with negative timestamps

In some specific timezones and operating systems, it seems that
getTimezoneOffset() can return an incorrect value for negative timestamps, as
described in #5017. While this isn't something easily fixed in the mock code,
the tests can avoid that particular timeframe by using a positive timestamp.

Closes #5017
Closes #6730
fix($rootScope): ng-repeat can't handle NaN values. #4605

$watchCollection checks if oldValue !== newValue which does not work for NaN. This was causing
infinite digest errors, since comparing NaN to NaN in $watchCollection would always return false,
indicating that a change was occuring on each loop.

This fix adds a simple check to see if the current value and previous value are both NaN, and
if so, does not count it as a change.

Closes #4605
Merge branch 'master' of https://github.com/angular/angular.js into 6749

* 'master' of https://github.com/angular/angular.js:
  fix($rootScope): ng-repeat can't handle NaN values. #4605
  test(ngMock): workaround issue with negative timestamps
  fix(select): avoid checking option element selected properties in render
  fix(orderBy): support string predicates containing non-ident characters
  fix(ngCookie): convert non-string values to string
  fix(ngTouch): update workaround for desktop Webkit quirk
  fix($httpBackend): don't error when JSONP callback called with no parameter
  fix($$RAFProvider): check for webkitCancelRequestAnimationFrame
  docs(tutorial/step_05): fix services link
  docs(tutorial/step_05): removed stray "a"
  style(ngMocks): remove ws
  feat(ngMock.$httpBackend): added support for function as URL matcher
  feat($compile): add support for $observer deregistration
  fix(Scope): $watchCollection should call listener with oldValue
  chore(log): add `log.empty()`  method to the testing logger