Core: Focus invalid element when validating a custom set of inputs

Invalid element is not focused when validate a custom set of inputs and
the last one is a valid input. The issue is element method, via
prepareElement method, via reset method, resets errorList state after
validate each input so the global state of the validator is not
preserved.

Closes #1327

src/core.js

@@ -90,16 +90,19 @@ $.extend($.fn, {
 	},
 	// http://jqueryvalidation.org/valid/
 	valid: function() {
-		var valid, validator;
+		var valid, validator, errorList;
 
 		if ( $( this[ 0 ] ).is( "form" ) ) {
 			valid = this.validate().form();
 		} else {
+			errorList = [];
 			valid = true;
 			validator = $( this[ 0 ].form ).validate();
 			this.each( function() {
 				valid = validator.element( this ) && valid;
+				errorList = errorList.concat( validator.errorList );
 			});
+			validator.errorList = errorList;
 		}
 		return valid;
 	},