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
chore($parse): micro-optimization for ensureSafeObject function

This version matches the "alternate 2.2" version here: http://jsperf.com/ensuresafeobject/2

alternate 2.3 is a bit faster and simpler, but would break backwards compatibility.

Closes #5246
fix(ngSanitize): prefer textContent to innerText to avoid layout trashing

innerText depends on styling as it doesn't display hidden elements.
Therefore, it's better to use textContent not to cause unnecessary
reflows. However, IE<9 don't support textContent so the innerText
fallback is necessary.