[GTK] Bump version

Reviewed by Carlos Garcia Campos.

* Source/autotools/Versions.m4: Bump to 2.3.0

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@156269 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Unify code paths leading to render tree teardown.
<https://webkit.org/b/121785>

Reviewed by Antti Koivisto.

Make Document::prepareForDestruction() fit all the call sites that were
doing destroyRenderTree() + disconnectFromFrame().

- disconnectDescendantFrames() is already a no-op if there are no frames.
- willDetachDocumentFromFrame() will only run if there is a frame.

This is another step towards making tree rebuild possible.

Removed some age-old FIXMEs about why we aren't calling willRemove(),
a long-gone function.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@156270 268f45cc-cd09-0410-ab3c-d52691b4dbfc