Unreviewed. Update NEWS and Versions.m4 for 2.4.0 release.

.:

* Source/autotools/Versions.m4: Bump version numbers.

Source/WebKit/gtk:

* NEWS: Added release notes for 2.4.0.

git-svn-id: http://svn.webkit.org/repository/webkit/releases/WebKitGTK/webkit-2.4@166163 268f45cc-cd09-0410-ab3c-d52691b4dbfc