perf(input): prevent multiple $digest when input is blurred

@kevinjamesus86 noticed that the input control would trigger a $digest
cycle every time it was blurred, https://github.com/angular/angular.js/commit/adcc5a00bf582d2b291c18e99093bb0854f7217c#commitcomment-7129512.

After the control is in a $touched state, other $digest cycles are
unnecesary.

References #7673
Why not $evalAsync or $timeout instead?

Using `$apply`, at least in [our directive](https://github.com/angular-ui/ui-select/issues/124) is causing `Error: [$rootScope:inprog] $apply already in progress` since we are [setting focus](https://github.com/angular-ui/ui-select/blob/ac79f4daee217e1a36b2e9e574502dd0eca3ae34/src/select.js#L240) to other input during a current $apply which will at the same time make this blur event run and cause the error.

Here's [plunker](http://plnkr.co/edit/EGMvHpuM1HAVMm77ldjC?p=preview) with the problem