fix(input): don't perform HTML5 validation on updated model-value

Running html5-validation immediately after model-value is updated is incorrect, because the view
has not updated, and HTML5 constraint validation has not adjusted.

Closes #6796
Closes #6806
fix(filter.ngdoc): Check if "input" variable is defined

By default, "greeting" textfield in this example is prepopulated with "hello" text, but it's pretty easy to copy just filter code to use it in your app. If your textfield is empty while app loads, you'll get an error: "Error: [$interpolate:interr] Can't interpolate: Reverse: {{greeting|reverse}} TypeError: Cannot read property 'length' of undefined". To prevent this, we should check "input" variable, and proceed only in case it is defined.

Closes #6819.
docs($http): fix auth default headers example
docs(guides/directive): add (') to contraction


add apostrophe (') to contraction