implement void nodes properly

Hello @eford1, @kylehardgrave, 

Please review the following commits I made in branch 'nick-optional5'.

93e3058843c3668387bcb72c927dc312e39bbcb1 (2013-08-05 18:19:58 -0400)
Add some documentation on configure()

f6b4b71674a1a2393623354b0cd8fcaef8406e61 (2013-08-05 18:19:58 -0400)
Implement void nodes properly


R=@eford1
R=@kylehardgrave