fix(jqLite): ignore incompatible nodes on find()

When a jqLite collection contains text nodes, find() does not work :-(

This fix ignores all nodes than can't do getElementsByTagName()

It seems a little bit faster than testing nodeType : http://jsperf.com/nodetype-vs-duck-typing

Closes #4120
Merge branch 'master' of https://github.com/angular/angular.js
componentizd!