Replace widget parent node - Issue 120

https://github.com/Matt-Esch/virtual-dom/issues/120
* widgetPatch can update parentNodes
* replaced DOM assert.equals at test/keys ("widgets can be keyed") with assertEqualDom
Fixed  as of https://github.com/Matt-Esch/virtual-dom/commit/687f846b517559d5b85a95ea5ec0e9039794d939. Sorry about that!