Makes singleton nodes work better with important nodes.

Hello @kylehg, @giannic, 

Please review the following commits I made in branch 'nick-singleton'.

320d6722041c8262bc8652f11a6ac48e85fbe3ed (2014-08-15 12:57:32 -0400)
Makes singleton nodes work better with important nodes.

R=@kylehg
R=@giannic
Missing test?