Regression: FilteringSelect throws error on create()

[haysmark]

With the new attr changes, FilteringSelect no longer loads: ​http://archive.dojotoolkit.org/nightly/checkout/dijit/tests/form/test_FilteringSelect.html

Seems that create() calls setValue before MappedTextbox's valueNode is generated in postCreate.

[bill]

Yah, sorry about that. Perhaps the attr() calls should occur after postCreate() although that might cause other problems. Will investigate.

[bill]

(In [14821]) Make MappedTextBox? do it's magic as part of buildRendering() rather than postCreate(). It's adding another node to the DOM so it really _should_ be part of buildRendering().

This fixes the FilteringSelect? initialization issue although it's still debatable whether all the attr() setter calls should happen before or after postCreate(), or inside _Widget.postCreate().

Also moved the attr() setter calls into a private method, in case that needs to be overridden.

Refs #7244, fixes #7414. !strict

[bill]

(In [14822]) Changes to disabled state should be reflected to hidden <input> as well.

Refs #7244, fixes #7414. !strict