Do not store 'mute_until' setting as item in the comments settings dictionary. Use a top level dictionary for it.

git-svn-id: http://ios.svn.wordpress.org/trunk@4088 7d847f7c-ffe1-4a24-85be-b788d016d96a
Bumped version number to 3.5.1 (Needed to enable and test the PNs muting feature).

git-svn-id: http://ios.svn.wordpress.org/trunk@4089 7d847f7c-ffe1-4a24-85be-b788d016d96a