Make Node.textContent ignore comment nodes

Currently it is incorrectly including the text from comment nodes in generating textContent.
Fix issues with innerHTML in plaintext like elements

This also cleans up innerHTML escaping for attributes, text nodes
and comments.
Merge pull request #346 from blois/fix_textContent

Make Node.textContent ignore comment nodes
Fix issue with Element not having all the required properties
Merge pull request #350 from arv/svg-tag-name

Fix issue with Element not having all the required properties
Fix element issue again
Merge pull request #351 from arv/fix-element-again

Fix element issue again
Fix issue related to matches and jQuery
Merge pull request #352 from arv/document-element-matches

Fix issue related to matches and jQuery
Implement Text.prototype.splitText
Merge pull request #355 from arv/split-text

Implement Text.prototype.splitText
Fix issue where the DOM tree could get out of sync.

The problem occurs when a node that requires invalidation is moved into
anohter node that does not require invalidation. The internal pointers
are no updated as expected.

Fixes https://github.com/Polymer/platform/issues/48
Merge pull request #348 from arv/script-inner-html

Fix issues with innerHTML in plaintext like elements
Merge pull request #356 from arv/dom-invalidation

Fix issue where the DOM tree could get out of sync.
Fix IE9 issue with shadow tree composition

msMatchesSelector does not work on elements that are not in the document
Fix IE9 issue with innerHTML on plaintext elements

Setting innerHTML on plaintext elements creates non Text children.
Check if the element is a plaintext elemend and if so use textContent
instead.
Merge pull request #362 from arv/fix-ie-9-matches

Fix IE9 issue with shadow tree composition
Add Selection interface
Merge pull request #363 from arv/fix-ie-9-inner-html

Fix IE9 issue with innerHTML on plaintext elements
Merge pull request #360 from arv/selection-interface

Add Selection interface