placeHolder text not being removed on set value

[Douglas Hays]

I added the following to dijit/tests/form/test_validate.html

<button onclick="dijit.byId('q26').set('value', 'value')">set value over placeHolder</button>

Load the test file and click the button and the placeHolder text remains after the set value, overlayed with the real value.

[liucougar]

(In [22144]) fixes #11131: programatically setting value on textbox should hide placeholder added a functional test