perf($http): move xsrf cookie check to after cache check in $http

$http was previously checking cookies to find an xsrf-token prior to checking
the cache. This caused a performance penalty of about 2ms, which can be very
significant when loading hundreds of template instances on a page.

Fixes #7717
docs(guide/bootstrap): fix link to angular.js  script in example

code.angularjs.org/angular.js is 404, updated it

Updated http://code.angularjs.org/angular.js in the example to http://code.angularjs.org/snapshot/angular.js
It works fine now.

Closes #7807
docs(TRIAGING.md): clarification for issues that are not reproducable
fix($injector): report circularity in circular dependency error message

Change the error message for a circular dependency to display the full
circle back to the first service being instantiated, so that the problem
is obvious. The previous message stopped one dependency short of the full
circle.

Changes the content of the cdep error message, which may be considered
a breaking change.

Closes #7500
feat(NgModel): introduce the $validators pipeline
fix(NgModel): make sure the required validator uses the $validators pipeline

Fixes #5164
fix(NgModel): make sure the pattern validator uses the $validators pipeline
fix(NgModel): make sure the ngMinlength and ngMaxlength validators use the $validators pipeline

Fixes #6304
fix(NgModel): make ngMinlength and ngMaxlength as standalone directives

Fixes #6750
fix(NgModel): ensure pattern and ngPattern use the same validator

When the pattern and ng-pattern attributes are used with an input element
containing a ngModel directive then they should both use the same validator
and the validation errors of the model should be placed on model.$error.pattern.

BREAKING CHANGE:

If an expression is used on ng-pattern (such as `ng-pattern="exp"`) or on the
pattern attribute (something like on `pattern="{{ exp }}"`) and the expression
itself evaluates to a string then the validator will not parse the string as a
literal regular expression object (a value like `/abc/i`).  Instead, the entire
string will be created as the regular expression to test against. This means
that any expression flags will not be placed on the RegExp object. To get around
this limitation, use a regular expression object as the value for the expression.

    //before
    $scope.exp = '/abc/i';

    //after
    $scope.exp = /abc/i;
docs(forms): additional documentation for $touched vs $pristine states
fix($compile): ensure transclude works at root of templateUrl

If a "replace" directive has an async template, which contains a transclusion
directive at its root node, then outer transclusions were failing to be
passed to this directive.  An example would be uses of `ngIf` inside and
outside the template.

Collaborated with @caitp

Closes #7183
Closes #7772
fix($parse): Handle one-time to `null`

Handles when a one-time binding stabilizes to `null`

Closes #7743
Closes #7787
docs(CONTRIBUTING.md): fix link to unit testing docs

The old link points to a page that doesn't exist

Closes #7830
perf(Scope): change Scope#id to be a simple number

In apps that create lots of scopes (apps with large tables) the uid generation
shows up in the profiler and adds a few milliseconds. Using simple counter
doesn't have this overhead.

I think the initial fear of overflowing and thus using string alphanum sequence
is unjustified because even if an app was to create lots of scopes non-stop,
you could create about 28.6 million scopes per seconds for 10 years before
you would reach a number that can't be accurately represented in JS

BREAKING CHANGE: Scope#$id is now of time number rather than string. Since the
id is primarily being used for debugging purposes this change should not affect
anyone.
perf(forEach): cache array length

Micro-optimization :-)

BREAKING CHANGE: forEach will iterate only over the initial number of items in
the array. So if items are added to the array during the iteration, these won't
be iterated over during the initial forEach call.

This change also makes our forEach behave more like Array#forEach.
perf(shallowCopy): use Object.keys to improve performance

This change is not IE8 friendly
perf(jqLite): don't use reflection to access expandoId

Since we allow only one copy of Angular to be loaded at a time it doesn't
make much sense randomly generate the expando property name and then be
forced to use slow reflective calles to retrieve the IDs.
fix(jqLite): data should store data only on Element and Document nodes

This is what jQuery does by default: https://github.com/jquery/jquery/blob/c18c6229c84cd2f0c9fe9f6fc3749e2c93608cc7/src/data/accepts.js#L16

We don't need to set data on text/comment nodes internally and if we don't
allow setting data on these nodes, we don't need to worry about cleaning
it up.

BREAKING CHANGE: previously it was possible to set jqLite data on Text/Comment
nodes, but now that is allowed only on Element and Document nodes just like in
jQuery. We don't expect that app code actually depends on this accidental feature.
perf(jqLite): optimize element dealocation

Iterate only over elements and not nodes since we don't attach data or handlers
to text/comment nodes.