Minor bugfixes
use _label instead of _node
Merge branch 'master' of https://github.com/nltk/nltk
fixed unresolved reference bugs in nltk.draw.util
Merge branch 'master' of https://github.com/nltk/nltk
Merge pull request #511 from usami/master

Remove unnecessary whitespaces before end of line
Merge pull request #513 from jskda/master

fixed unresolved reference bugs in nltk.draw.util