Update NaCl SDK release notes.

M33 branched on December 16th 2013, update the NaCl SDK release notes to mention libc++ and sjlj EH.

R= sbc@chromium.org, binji@chromium.org, mackinlay@chromium.org, sehr@chromium.org, awatson@chromium.org
BUG= N/A
TEST= N/A
NOTRY=true
(documentation only change)

Review URL: https://codereview.chromium.org/118313005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241920 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241920